Asexual reproduction. sexual reproduction

"Fundamentals of General Biology Textbook for Grade 9 Students educational institutions Third edition, revised edited by prof. I.N. Ponomareva Recommended...»

-- [ Page 2 ] --

Cell division is a complex process of asexual reproduction. The resulting new daughter cells usually become capable of dividing after a certain period of their development. This is due to the fact that division should be preceded by doubling of intracellular organelles that ensure the vital activity of the cell. Otherwise, fewer and fewer organelles would get into the daughter cells. For normal functioning, a daughter cell, like a parent cell, must receive hereditary information about its main features contained in chromosomes. Without this information, the cell will not be able to synthesize the nucleic acids and proteins that it needs. And this means that each daughter cell during division needs to receive a copy of the chromosomes with hereditary information from the parent cell.

Self-reproduction by division - common property cells of unicellular and multicellular organisms. However, this process occurs differently in prokaryotic and eukaryotic cells.

Cell division in prokaryotes. Cell division of prokaryotes is due to the peculiarities of the structure of their cells. Prokaryotic cells do not have a nucleus or chromosomes.

Therefore, cells multiply by simple division. The nuclear substance in bacteria is represented by a single circular DNA molecule, which is conventionally considered a chromosome. DNA is circular in shape and is usually attached to the cell membrane.

Before dividing, the bacterial DNA is duplicated, and each of them, in turn, is attached to the cell membrane. Upon completion of DNA duplication cell membrane grows between two DNA molecules formed. Thus, the cytoplasm is divided into two daughter cells, each of which contains an identical circular DNA molecule (Fig. 20).

Cell division in eukaryotes. In eukaryotic cells, DNA molecules are enclosed in chromosomes. Chromosomes play leading role during the process of cell division. They ensure the transfer of all hereditary information and participation in the regulation of metabolic processes in daughter cells. By distributing chromosomes between daughter cells and transferring to each of them a strictly identical set of chromosomes, continuity of properties is achieved in a number of generations of organisms.

When dividing, the nucleus of a eukaryotic cell goes through a series of sequentially and continuously following each other stages. This process is called mitosis (gr.

mitos- "thread").

As a result of mitosis, first doubling occurs, and then uniform distribution hereditary material between the two nuclei of the resulting daughter cells.

Depending on what happens in a dividing cell and how these events look under a microscope, there are four phases, or stages, of mitosis, following one after another: the first phase is prophase, the second is metaphase, the third is anaphase and the fourth, final, - telophase. Let's take a look at what's going on in the nucleus. different stages division (Fig. 21).

Prophase. Increased core size. The nuclear membrane disintegrates. Doubled chromosomes are clearly visible: they consist of two thread-like copies - chromatids, connected by a constriction - a centromere. In the cytoplasm, microtubules form an apparatus for pulling chromosomes apart - the division spindle.

Metaphase. Chromosomes move to the center of the cell. Each of them consists of two chromatids connected by a centromere. One end of the spindle threads is attached to the centromeres.

Anaphase. Microtubules contract, centromeres separate and move away from each other. The chromosomes separate and the chromatids move to opposite poles of the spindle.

Telophase. New nuclei are formed. Chromosomes in new nuclei become thin, invisible under a microscope. The nucleolus reappears and the shell of the nucleus is formed. This is the last phase of cell division.

Simultaneously with telophase, the division of the cytoplasm begins. First, a constriction (partition) is formed between the daughter cells. After some time, the contents of the cell are divided. This is how new daughter cells appear with cytoplasm around new identical nuclei. After that, the preparation for the division of the now new cell begins again, and the whole cycle is repeated continuously, if there are favorable conditions. The process of mitosis takes about 1-2 hours. Its duration varies in different types cells and tissues. It also depends on environmental conditions.

The division of the nucleus and, consequently, the cell goes on continuously as long as the cell has the means to ensure its vital activity.

Cell cycle. The existence of a cell from the moment it appears as a result of division to division into daughter cells is called the cell life cycle or cell cycle. There are two stages (or stages) in the cell life cycle.

The first stage of the cell cycle is preparing the cell for division. It is called interphase (from Latin inter- “between” and Greek phasis- “appearance”). Interphase in the cell cycle takes the longest (up to 90%) time interval. During this period, the nucleus and nucleolus are clearly visible in the cell. There is an active growth of a young cell, biosynthesis of proteins, their accumulation, preparation of DNA molecules for doubling and doubling (replication) of all chromosome material is carried out. Chromosomes are not visible, but the process of their doubling is actively going on. A doubled chromosome consists of two halves containing one double-stranded DNA molecule. Characteristic features of interphase cells are despiralization (unwinding) of chromosomes and their uniform distribution in the form of a loose mass throughout the nucleus. By the end of the interphase, the chromosomes spiralize (twist) and become visible, but still represent thin elongated threads (Fig. 22).

At the second stage of the cell cycle, mitosis occurs and the division of the cell into eukaryotes are methods of asexual reproduction: daughter cells receive the hereditary information that the parent cell had. Daughter cells are genetically identical to the parent. There are no changes in the genetic apparatus here. Therefore, all cells that appear in the process of cell division and the tissues formed from them have genetic homogeneity.

1. Explain the differences in the processes of cell division in prokaryotes and eukaryotes.

2*. Why are the offspring identical to the parent in asexual reproduction?

3. Describe the process of mitosis and the features of each of its stages.

4. Replace the underlined words with terms.

The first phase of mitosis begins when the chromosomes become visible.

At the end of the third phase of mitosis, the chromosomes are at opposite poles of the cell.

Cell structures containing genetic information become visible only during mitosis.

Laboratory work No. 2 (see Appendix, p. 230).

§ 15 Formation of sex cells. Meiosis Sex cells (gametes) develop in the reproductive (generative) organs and play an important role: they ensure the transfer of hereditary information from parents to offspring. During sexual reproduction, as a result of fertilization, two germ cells (male and female) merge and form one cell - a zygote, the subsequent division of which leads to the development of a daughter organism.

Imagine how many chromosomes would then accumulate in one cell!

But this does not happen in living nature: the number of chromosomes in each species during sexual reproduction remains constant. This is due to the fact that germ cells are formed by a special division. Due to this, not two (2n), but only one pair of chromosomes (In), that is, half of what was in the cell before its division, enter the nucleus of each germ cell. Cells with a single set of chromosomes, i.e.

The process of division of germ cells, as a result of which there are half as many chromosomes in the nucleus, is called meiosis (Greek meiosis - “reduction”).

A halving of the number of chromosomes in the nucleus (the so-called reduction) occurs during the formation of both male and female germ cells. During fertilization by fusion of germ cells in the nucleus of the zygote, a double set of chromosomes (2p) is again created.

It should be noted that in many eukaryotes (microorganisms, lower plants and males of some arthropod species) somatic (Greek soma - “body”) cells (all body cells, excluding sex cells) have a haploid set of chromosomes. In many flowering plants, the cells are polyploid, that is, they contain many sets of chromosomes. But in most animals, in humans and in higher plants, only germ cells are haploid. In all other cells of the body of these organisms, the nucleus contains a diploid (2p) - a double set of chromosomes.

Meiosis is of great importance in the living world. In the process of meiosis (unlike mitosis), daughter cells are formed that contain half as many chromosomes as the parent cells, but due to the interaction of the chromosomes of the father and mother, they always have new, unique combinations of chromosomes. These combinations in offspring are expressed in new combinations of traits. The emerging set of chromosome combinations increases the ability of a species to develop adaptations to changing environmental conditions, which is very important for evolution.

With the help of meiosis, germ cells are formed with a smaller set of chromosomes and with qualitatively different genetic properties than those of the parent cells.

The names of the phases are the same as the phases of mitosis. Interphases are observed before divisions.

But doubling of DNA in mitosis occurs only before the first division. The course of meiosis is shown in Figure 23.

In the first interphase (preceding the first division of meiosis), there is an increase in cell size, doubling of organelles and doubling of DNA in chromosomes.

The first division (meiosis I) begins with prophase /, during which duplicated chromosomes (having two chromatids each) are clearly visible under a light microscope. In this phase, identical (homologous) chromosomes, but originating from the nuclei of the paternal and maternal gametes, approach each other and “stick together” along the entire length into pairs. The centromeres (constrictions) of homologous chromosomes are located side by side and behave as a single unit, holding the four chromatids together. Such interconnected homologous doubled chromosomes are called a pair or bivalent (from Latin bi - “double” and valens - “strong”).

The homologous chromosomes that make up the bivalent are closely connected to each other at some points. In this case, an exchange of sections of DNA strands can occur, as a result of which new combinations of genes in the chromosomes are formed. This process is called crossing door (English cmssingover - “cross”). Crossing over can lead to recombination of large or small sections of homologous chromosomes with several genes or parts of one gene in DNA molecules (Fig. 24).

Due to crossing over, chromosomes with other hereditary properties in comparison with the chromosomes of parental gametes turn out to be in germ cells.

The phenomenon of crossing over is of fundamental biological importance, as it increases the genetic diversity in the offspring.

The complexity of the processes occurring in prophase I (in chromosomes, nucleus) determines the longest duration of this stage of meiosis.

In metaphase I, bivalents are located in the equatorial part of the cell. Then, in anaphase I, homologous chromosomes separate to opposite poles of the cell. Telophase / completes the first division of meiosis, as a result of which two daughter cells are formed, although each chromosome in them still remains doubled (that is, it consists of two sister chromatids).

Telophase I is followed by a second interphase. She takes very a short time because DNA synthesis does not occur in it.

In telophase II, around the nucleus, which now contains a single (haploid) set of chromosomes, the nuclear membrane re-forms and the cellular contents divide. The reduction process of the formation of germ cells ends with the creation of four haploid cells - gametes.

As a result of meiosis, four cells with a haploid set of chromosomes appear from one cell.

The process of formation of male germ cells (spermatozoa) is called spermatogenesis (from the Greek spermatos - "seed" and genesis - "emergence", "origin"). The process of development of female germ cells (eggs) is called oogenesis or oogenesis (from the Greek oop - “egg” and genesis - “emergence”, “origin”), 1. Why are the properties of daughter organisms that developed from a zygote not identical to those of the parent?

2*. What is the biological meaning of meiosis?

Cell division, as a result of which there are half as many chromosomes in the nucleus, leads to the formation of germ cells.

4. Complete the statement by choosing the correct term:

The same chromosomes from father and mother are called:

b) homologous; d) single.

§ 16 Individual development of organisms - ontogeny An organism undergoes significant transformations during the period of its life:

grows and develops.

The totality of transformations occurring in the body from its inception to natural death is called individual development or ontogeny (from the Greek ontos - “existing” and genesis - “emergence”, “origin”). In unicellular organisms, life fits into one cell cycle and all transformations occur between two cell divisions. In multicellular organisms, this process is much more complicated.

With asexual reproduction, including vegetative reproduction, ontogenesis begins from the moment of division of the initial (i.e., giving rise) cells of the mother's organism. The organism in the early stages of development is called the germ.

Unicellular organisms, like all cells, arise by cell division. In a newly formed cell, intracellular structures are not always formed that provide its specific functions and life processes. It takes a certain time for all organelles to form and all the necessary enzymes to be synthesized. This early period the existence of a cell (and a unicellular organism) in the cell cycle is called maturation. It is followed by a period of mature cell life, culminating in its division.

In the individual development of a multicellular organism, several stages are distinguished, which are often called age periods. There are four age periods: germinal (embryonic), youth, maturity and old age.

In animals, only two periods are often distinguished: embryonic and postembryonic. The embryonic period is the development of the embryo (embryo) before its birth. Post-embryonic is the period of development of an organism from its birth or exit from the egg or embryonic membranes to death.

The embryonic period of ontogenesis (embryonic development), occurring in utero in the mother's body and ending in birth, is found in most mammals, including humans. In oviparous and spawning organisms, embryonic development occurs outside the mother's body and ends with the exit from the egg membranes (in fish, amphibians, reptiles, birds, as well as in many invertebrate animals - echinoderms, molluscs, worms, etc.).

In the vast majority of animal organisms, the process of embryonic development occurs in a similar way. This confirms the commonality of their origin.

In humans, during embryonic development, the brain and spinal cord begin to separate first. This happens within the third week after conception. At this stage, the length of the human embryo is only 2 mm.

From the first days of embryonic development, the embryo is very sensitive to damaging effects, especially chemical (drugs, poisons, alcohol, drugs) and infectious. For example, if a woman falls ill with rubella between the 4th and 12th weeks of pregnancy, this can cause a miscarriage or disrupt the formation of the heart, brain, organs of vision and hearing in the fetus, i.e., organs whose development occurs in this period.

After the birth or exit from the egg, the postembryonic development of the organism begins. For some organisms, this period of life takes several days, for others - several tens and hundreds of years, depending on the species.

A person dies of old age between the ages of 75-100, although some people live to be over 100 years old.

Postembryonic development consists of three age periods:

youth, maturity and old age. Each of these periods is characterized by certain transformations in the structure and life processes of the organism, due to its heredity and the influence of external conditions.

In the process of postembryonic development, the organism undergoes quantitative and qualitative changes.

Ontogeny is the development of an individual (individual) due to heredity and the influence of environmental conditions.

Ontogeny is certainly one of the most amazing biological phenomena.

Having appeared in the form of a tiny embryo or germ, the body goes through a number of complex stages of development, during which all the organs and mechanisms that ensure vital activity are gradually formed in it. Having reached puberty, the organism realizes the main function of the living - it gives offspring, which ensures the duration and continuity of the existence of its species.

The existence of any organism is a complex and continuous process of embryonic and postembryonic development in certain habitat conditions and over the periods characteristic of each species.

1. Describe the period of embryonic development of the organism.

Replace the following definitions with terms: an organism in the early stages of development; individual development of a multicellular organism.

3*. Explain why the influence of dangerous external influences (radiation, smoking) is more destructive at the embryonic stage of ontogenesis than at the postembryonic stage.

Indirect cell division (mitosis) during the passage of a series of phases (prophase, metaphase, anaphase, telophase) ensures the transfer to daughter cells of the same hereditary information contained in the chromosomes of the nucleus as the parent. Interphase prepares the cell for division.

The most ancient type of reproduction is asexual reproduction. It ensures the stability of genetic information, the preservation of the properties of the species, a faster increase in numbers and resettlement to new territories.

Sexual reproduction arose in the process of evolution later than asexual.

Through meiosis, crossing over, and fertilization, sexual reproduction provides genetic variability that allows organisms to acquire new traits and properties, and thus better adapt to changing environmental conditions.

In the process of meiosis, the reduction division of germ cells and the formation of a haploid (In) set of chromosomes in the nucleus of gametes occur. When cells are fertilized, the male and female gametes merge with a haploid set of chromosomes and a zygote is formed with a diploid (2p) set of chromosomes in the nucleus.

The zygote gives rise to the development of a new organism. The course of an organism's life from birth to death is called individual development (ontogenesis). In multicellular organisms, ontogenesis consists of the embryonic and postembryonic periods.

The individual development of all organisms is carried out in accordance with the hereditary properties inherent in the species, and depending on the environmental conditions.

Check yourself 1. Explain the biological role of female and male sex gametes.

2. Explain the main differences between mitosis and meiosis.

3. What is the dependence of the individual development of the organism on environmental conditions in the embryonic and postembryonic periods?

4. What stages are observed in the cell cycle of unicellular organisms? Explain the importance of interphase in the life of a cell.

1. Describe the concepts of "growth of the organism" and "development of the organism."

Problems for discussion 1. Describe the biological role of different types of reproduction if they are observed in organisms of the same species. Give examples.

2. Expand the mechanism for ensuring the continuity of life.

3. Is it correct to say that the development of the organism occurs in the embryonic period, and in the postembryonic period there is only an increase in the size of the body, i.e., the growth of the organism? Support your opinions with concrete examples.

Basic concepts Asexual reproduction. Sexual reproduction. Gamete. Zygote. Chromosome. Mitosis. Meiosis. Crossing over. Cell cycle. diploid cell.

haploid cell. Ontogenesis.

Chapter of Variability After studying the chapter, you will be able to:

explain the basic concepts of genetics;

describe the mechanism of sex determination and types of trait inheritance;

characterize the role of heredity and variability of organisms in wildlife.

§ 17 From the history of the development of genetics Genetics (Greek genesis - “origin”) is the name of the science that studies the heredity and variability of organisms, as well as the mechanisms for controlling these processes. It has a long history.

Even in ancient times, people understood that plants, animals, and even humans inherit some characteristics from their parents, since it was impossible not to see the similarities between offspring and parents. Moreover, certain "generic" signs were passed on unchanged from generation to generation. Based on this ability of plants and animals to inherit certain qualities, they began to select plant seeds for sowing from the most productive individuals, tried to keep young animals that have the properties that people need - giving more milk or wool, better performing draft work, etc.

Ancient Chinese manuscripts testify, for example, that 6,000 years ago, different varieties of rice were created through crossbreeding and selection. Archaeological finds confirm that the Egyptians cultivated productive varieties of wheat. Among the Babylonian written monuments in Mesopotamia, a stone tablet was found dating back to the 6th millennium BC. e., which recorded data on the inheritance of the shape of the head and mane in five generations of horses (Fig. 25).

However, only in the 19th and early 20th centuries, when knowledge about the life of the cell was accumulated, scientists began to study the phenomenon of heredity. First treatise on the study of heredity was carried out by the Czech scientist and monk G. Mendel. In 1865, in the article "Experiments on plant hybrids," he formulated the patterns of inheritance of traits that laid the foundation for the science of genetics. Mendel showed that hereditary traits (inclinations) are not "fused", as previously thought, but are transmitted from parents to descendants in the form of discrete (isolated, separate) units, which he called factors. These units, presented in pairs in individuals, do not merge together, but remain discrete and are transmitted to descendants in male and female germ cells, one unit from each pair.

In 1909, hereditary units were named by the Danish scientist V.

Johansen genes (Greek genos- "genus"). At the beginning of the XX century. the American embryologist and geneticist T. Morgan established experimentally that genes are located on chromosomes and are arranged linearly there. Since then, the concept of the gene has been central to genetics.

Prominent role in the development of genetics in the first half of the XX century. played by our domestic scientists.

A.S. Serebrovsky, exploring the genetics of animals, showed the complex structure of the gene, introduced the term "gene pool" into science. The doctrine of heredity and variability was enriched by the works of N.I. Vavilov, who formulated in 1920 the law of homological series of heredity and variability, which ensured a close connection between genetics and evolutionary doctrine. Yu.A. Filipchenko conducted numerous experiments on the genetic analysis of plants, developed methods for studying variability and heredity. A significant contribution to the development of genetics was also made by G.D.

Karpechenko, N.K. Koltsov, S.S. Chetverikov and other researchers.

In the 40s. the biochemical foundations of genetics were laid. Scientists have proven the role of molecules nucleic acids in the transmission of hereditary information, which led to the birth of molecular genetics. Deciphering the structure of the DNA molecule, published in 1953, showed a close connection of this chemical compound with hereditary information in genes.

Advances in molecular genetics have led to the creation of a new branch of biological science - genetic engineering, which allows, by manipulating individual genes, to obtain in vitro new combinations of genes in the chromosome, which were not there before. Genetic engineering has become widely practiced Agriculture and biotechnology.

The development of genetics based on molecular bases in the consideration of hereditary qualities became possible thanks to the creation of high technologies in the field of scientific research, which appeared only in the middle of the 20th century.

Genetics is theoretical basis selection (lat. selectio - “choice”, “selection”) of plants, animals and microorganisms, i.e. the creation of organisms with the properties that a person needs. Based on genetic patterns, breeders create improved plant varieties and breeds of domestic animals. Genetic engineering methods produce new strains (pure cultures) of microorganisms (bacteria, fungi) that synthesize substances for the treatment of diseases.

The research of genetic scientists has led to the understanding of the fact that along with infectious diseases There are many different hereditary diseases. Early diagnosis of these diseases allows timely intervention in the course of the disease and prevent or slow down its development.

Environmental degradation and negative environmental changes have caused many disorders in the genetic sphere of living organisms, increasing the likelihood of hereditary diseases in humans.

To solve many of the problems associated with this alarming trend, and to ensure human genetic security, targeted research and the combined efforts of ecologists and geneticists were required. Thus, a new important direction in science arose - ecological genetics, which ensured the development of the genetic security service. The latter studies the genetic activity of chemical and physical environmental factors that affect humans and nature as a whole. Ecologists have proved that for the sustainable development of life on Earth it is necessary to preserve the biological diversity of species and natural ecosystems. This vital task for humanity has led to the active development of such a direction in biological science as population genetics.

Knowledge of genetics is in demand in botany, zoology, microbiology, ecology, evolution, anthropology, physiology, ethology and other areas of biology. Genetic research data is used in biochemistry, medicine, biotechnology, nature conservation, and agriculture. It can be said that the discoveries and methods of genetics find application in all areas of human activity related to living organisms. The laws of genetics are of great importance for explaining all the processes of life on Earth.

The scientific and practical role of genetics is determined by the significance of the subject of its study - heredity and variability, that is, the properties inherent in all living beings.

1. What does the science of genetics study, when and why did it get its name?

2. Why is G. Mendel considered the "father of genetics"?

3. Replace the highlighted words with the term.

The data of science, which studies the heredity and variability of organisms, are now widely used in all areas of biology.

Units that ensure the transfer of hereditary properties are present in all organisms without exception.

4*. Describe the role of knowledge about nucleic acids for the development of genetics.

§ 18 Basic concepts of genetics Genetics studies two basic properties of living organisms - heredity and variability.

Heredity is the ability of organisms to transmit their characteristics and characteristics of development to offspring. Thanks to this ability, all living beings (plants, animals, fungi or bacteria) retain in their descendants character traits kind. Such continuity of hereditary properties is ensured by the transfer of their genetic information. Genes are the carriers of hereditary information in organisms.

A gene is a unit of hereditary information that manifests itself as a sign of an organism.

In the topic “Protein biosynthesis in a living cell” (§ 10), it was noted that a gene serves as the basis for building protein molecules, but in genetics, a gene acts as a carrier of a trait in an organism. This “duality” of the gene becomes understandable if we recall that the most important function of a protein in a cell is enzymatic, that is, the control of chemical reactions, as a result of which all the signs of an organism are formed. This "dual" role of the gene can be expressed by the scheme: gene - protein - enzyme - chemical reaction - a sign of the organism.

A gene is a section of a DNA molecule (and in some viruses, RNA) with a certain set of nucleotides. The sequence of nucleotides contains genetic information about the development of the characteristics of an organism. In higher organisms, genes are located in the DNA of chromosomes (these are the so-called nuclear genes) and in the DNA contained in the organelles of the cytoplasm - mitochondria and chloroplasts (these are cytoplasmic genes).

In all organisms of the same species, each gene is located in a certain place relative to other genes. The location of a gene on a stretch of DNA is called a locus. In different individuals of the same species, each gene has several forms - alleles. Alleles contain information about one or another variant of the development of a trait that is controlled by this gene (for example, eye color). The cells of a diploid organism usually contain two alleles of each gene, one received from the mother, the other from the father. Any change in the structure of a gene leads to the appearance of new alleles of this gene and a change in the trait controlled by it.

Organisms that carry different (alternative) alleles of the same gene on the same (homologous) chromosomes are called heterozygous, and organisms with the same alleles on homologous chromosomes are called homozygous.

Heterozygosity usually ensures a higher viability of organisms, their good adaptability to changing environmental conditions, and therefore is widely represented in natural populations of various species.

A gene is a section of a DNA molecule that determines the possibility of developing a particular trait. However, the very development of this feature is largely dependent on external conditions.

The totality of all genes (alleles) of an individual is called the genotype.

The genotype acts as a single interacting system of all genetic elements that control the manifestation of all the signs of the organism (development, structure, vital activity).

The totality of all the characteristics of an organism is called the phenotype. The phenotype is formed in the process of interaction between the genotype and the external environment. Not all genotypic possibilities of an organism are realized in the phenotype. Therefore, the phenotype is also called a special case of the manifestation of the genotype in specific conditions. There is practically no complete coincidence of the genotype with the phenotype. A change in the genotype is not always accompanied by a change in the phenotype, and vice versa.

Within the same species, all individuals are quite similar to each other. But under different conditions, individuals, even with the same genotype, can differ among themselves in the nature and strength of the manifestation of their characteristics (i.e., in phenotype). In this regard, in genetics, the concept of the reaction norm is used, which denotes the range (limits) of the phenotypic manifestations of a trait in an individual under the influence of the external environment without changing the genotype.

The genotype determines the limits (range) of the norm of the reaction of the organism, i.e., its genetic capabilities, and the phenotype implements these capabilities in signs.

Therefore, the manifestation of signs even in closely related organisms can be different. These differences between individuals within a species are called variability.

Variability is a property of living organisms to exist in various forms, providing them with the ability to survive in changing environmental conditions.

Variation can be caused by the influence of environmental factors that do not affect changes in the genotype. The variability associated with changes in the genotype is accompanied by the appearance of new traits and qualities inherited by the organism. This is especially often observed in individuals that have appeared as a result of crossing.

Variation is a property of organisms, opposite to heredity.

But both heredity and variability are inextricably linked. They ensure the continuity of hereditary properties and the ability to adapt to changing new environmental conditions, causing the progressive development of life.

Heredity and variability are inherent in all organisms. Genetics, studying the patterns of heredity and variability, reveals methods for managing these processes.

1. What is an allele? What genes are called allelic?

2. Compare the role of heredity and variability in the life of organisms.

3*. Eliminate words in sentences that distort the correctness of the statements.

Gene like hereditary factor and a discrete unit of genetic information is localized in the chromosomes of organelles.

A genotype is a single system of all chromosomes and genetic elements of a given cell or organism.

The limits of the reaction norm are determined by the genotype and phenotype.

A phenotype is a collection of traits and genes of an organism.

§19 Mendel's genetic experiments Man has always tried to find out the patterns of inheritance of traits.

Based on many years of practice, talented breeders obtained exactly the properties that they wanted to see in a new plant variety (for example, apple trees, roses) or animal breeds (horse color, dog body shape, dove, rooster tail length, etc.). However, for a long time no one was able to explain how genetic information is transmitted from parents to offspring. Only in the middle of the XIX century. in the Czech city of Brno, the monk G. Mendel, thanks to genetic experiments, answered this question.

Mendel thought out the conditions for conducting genetic experiments well and chose a very successful object of study - peas.

researcher with a combination of properties. In this case, crossing will occur - the union as a result of the sexual process of the genetic material of two cells in one cell. An organism with new hereditary properties that has developed from such a cell is called a hybrid (Latin hibrida - "crossbreed"). By crossing in this way plants of two varieties with contrasting traits (Fig. 26), Mendel carried out an accurate account of the inheritance of these traits in a number of generations.

As a result of many years of preliminary experiments, he selected pure lines from many varieties of peas, which differed in a number of contrasting features.

Mendel chose seven such traits that have a contrasting manifestation in the offspring: 1) flower color (purple and white); 2) seed color (yellow and green); 3) coloring of beans (green and yellow); 4) seed surface (smooth and wrinkled); 5) the shape of the beans (simple and segmented); 6) stem length (long and short); 7) the position of flowers on the stem (axillary and apical).

At first, he studied the inheritance of one pair of contrasting variants of only one trait.

Crossing, in which parents differ in one trait, Mendel called monohybrid. Having studied the manifestation of one discrete trait, differences in which are inherited alternatively, he moved on to studying the transmission of two traits (dihybrid crossing), and then three traits (trihybrid crossing). Checking his conclusions through numerous experiments and quantitative accounting of all types of hybrids obtained, and then carefully analyzing the results, the researcher identified patterns of inheritance of traits.

Mendel's first law. First, experiments were carried out on crossing peas with purple and white flowers. Mendel pollinated purple flowers with pollen from white flowers and vice versa. With such a crossing of two genetically different varieties, a mixed offspring was obtained - hybrids of the first generation.

Mendel discovered that by crossing pea varieties with purple and white flowers, all plants in the first generation turned out to be the same (uniform) - with purple flowers (Fig. 27).

Mendel made the ingenious assumption that each inherited trait is transmitted by its own factor (later called the gene). In pure lines of peas, each parent has one trait: the flower is either white or purple. The hybrids simultaneously contain the signs of both parents, but only one of them, the more “strong”, appears outwardly. He called such a “strong” sign dominant (lat. dominantis - “dominant”), and “weak” - recessive (lat. recessus - “removal”). In the case of purple and white pea flowers, the purple color of the flowers turned out to be the dominant trait, and the white color was the recessive trait.

To designate signs, Mendel introduced literal symbolism, which is still used today. He designated dominant genes in capital letters, and recessive genes in the same but lowercase letters of the Latin alphabet. So, he designated the purple color of the pea flower (dominant trait) A, and the white color of the flower (recessive trait) - a. He designated the parents P, the crossing - the sign "x", and the hybrids of the first generation - F,.

Consider the genotype of the parents in this experiment. Pure varieties are characterized by the homogeneity of paired (allelic) genes, i.e., parental individuals (P) contained inclinations (allelic genes) of only one type: either recessive (aa) or dominant (AA). Such individuals are called homozygous (from the Greek homos - “same” and “zygote”), and individuals with different hereditary inclinations (Aa) are called heterozygous (from the Greek heteros - “other” and “zygote”).

In plants with white flowers, both allelic genes are recessive, that is, they are homozygous for the recessive trait (aa). With self-pollination, such offspring in all subsequent generations will be exclusively with white flowers. Parental plants with purple flowers carry the same allelic genes - they are homozygous for the dominant trait (AA), and their descendants will always be purple. When crossing hybrids of the first generation, each allele receives one gene from both parents. But in such hybrids, only the dominant trait (purple flowers) appears, and the recessive trait (white flowers) is masked. Therefore, all first-generation hybrids look the same - purple.

The same regularity was also observed in experiments on other traits: in all hybrids of the first generation, only one, dominant trait appears, and the second, recessive, seems to disappear. Mendel called the revealed pattern the rule of dominance, which is now called the law of uniformity of hybrids of the first generation or Mendel's first law.

Mendel's first law states: when crossing parents of pure lines that differ in one contrasting trait, all hybrids of the first generation will be uniform and they will show the trait of only one of the parents.

The dominant gene in the heterozygous state does not always completely mask the recessive gene.

There are cases when the hybrid F (is of an intermediate nature - with incomplete dominance.

For example, when crossing a night beauty with red (AA) and white (aa) flowers in hybrids (F j), the color of the flowers (Aa) was intermediate - pink (incomplete dominance). This intermediate type of inheritance of traits is often observed in animals (Fig. 28).

Mendel's second law. Having received the hybrid seeds of the first generation of peas, Mendel sowed them again, but now he did not re-pollinate. As a result of self-pollination, the plants produced seeds of the second generation (F2). Among them were plants with purple flowers (there were most of them) and with white flowers (about a quarter of the plants).

Mendel found that during self-pollination of hybrids of the first generation, dominant and recessive traits appear in offspring in various combinations. This is expressed in the genotype as follows: one homozygous for a dominant trait (AA), two heterozygotes (Aa) and one homozygous for a recessive trait (a a). Outwardly, that is, in the phenotype, this manifests itself as follows: three individuals with purple flowers and one with white ones. The phenomenon in which, as a result of crossing heterozygous individuals, the distribution of dominant and recessive traits in the offspring occurs in a ratio of 3: 1 was called splitting by Mendel. Nowadays, this phenomenon is called the splitting law or Mendel's second law.

Mendel's second law states: when two hybrids of the first generation are crossed among themselves, among their descendants - hybrids of the second generation - splitting is observed: the number of individuals with a dominant trait is related to the number of individuals with a recessive trait as 3: 1.

According to this law, hybrids of the first generation give splitting: individuals with recessive traits reappear in their offspring, making up about a quarter of the total number of offspring.

The law of splitting is common to all living organisms.

Mendel explained the splitting of traits in offspring when heterozygous individuals were crossed by the fact that in their germ cells (gametes) there is only one deposit (gene) from an allelic pair, which behaves as independent and whole.

Mendel called this phenomenon the purity of gametes, although he did not know why this happened. And this is understandable: in his time, nothing was known about either mitosis or meiosis. It has now been established that due to meiosis, a haploid (single) set of unpaired chromosomes is formed in gametes, and either dominant or recessive genes are located in them.

1. Explain the essence of Mendel's first law.

2. Formulate the second law of Mendel.

3*. What is the difference between F; from F2 in a monohybrid cross?

4*. Why are alleles always paired?

§ 20 Dihybrid crossing. Mendel's third law Having established the law of splitting on the example of monohybrid crosses, Mendel began to find out how pairs of alternative traits of a gene behave. After all, organisms differ from each other not in one, but in many ways.

In order to establish the mechanism of inheritance of two pairs of alternative traits, he conducted a series of experiments on dihybrid crossing. For experiments, peas with smooth yellow seeds were taken as the mother plant, and green wrinkled seeds were taken as the father plant. In the first plant, both traits were dominant (AB), and in the second, both traits were recessive (ab).

As a result of crossing, according to the law of trait dominance, in hybrids of the first generation (F j), all seeds turned out to be smooth and yellow. On the next year plants grew from these seeds, in the flowers of which self-pollination occurred. In plants obtained in this way (second generation - F 2), there was a splitting of characters, and along with the parental ones (smooth yellow and wrinkled green seeds), completely new ones appeared - wrinkled yellow and smooth green seeds.

It turned out that heterozygotes for two pairs of allelic genes form four types of gametes in equal amounts (AB, Ab, aB, ab). In two of them, the genes are in the same combination as in the parents, and in the other two - in new combinations, or recombinations. The ratio of genotypic forms of F2 hybrids (Fig. 29) can be established using the Punnett lattice, named after one of the prominent English geneticists of the early 20th century, who proposed this method. In the grid, the allelic genes of the gametes of the parents are written horizontally and vertically and, by combining them, the genotypes of the offspring are obtained in the windows.

The identification of these patterns is possible only with a very large amount of experimental material, therefore, Mendel, studying the splitting of seeds on the basis of the shape of the seeds, studied 7324 peas, on the basis of color - peas, and on the basis of shape and color - 556.

In the dihybrid cross under consideration, hybrid seeds (556 pieces) of the second generation (F2) split in the following ratio: 315 smooth yellow, 108 smooth green, 101 wrinkled yellow and 32 wrinkled green. This distribution of peas showed that 3/4 of them are yellow, and 1/4 of them are green. Among the yellow seeds, 3/4 were smooth and 1/4 were wrinkled. In greens, the same ratio was observed: 3/4 smooth and 1/4 wrinkled. In all cases, the results showed a ratio of 3:1.

Experiments on dihybrid crossing showed that the splitting of one pair of traits (yellow and green) is not at all related to the splitting of the other pair (smooth and wrinkled form). This means that two pairs of traits are redistributed independently of each other during transmission from generation to generation. At the same time, the seeds of F2 hybrids were characterized not only by parental combinations of traits, but also by recombinations (new combinations).

Analyzing the results of dihybrid crossing, Mendel concluded:

splitting in both pairs of contrasting (alternative) features occurs independently of each other. This phenomenon reflects the essence of Mendel's third law - the law of independent inheritance (combination) of traits.

Mendel's third law states that each pair of contrasting (alternative) traits is inherited independently from each other in a number of generations; as a result, among the hybrids of the second generation, descendants with new combinations of traits appear in the ratio of 9:3:3:1.

The law of independent inheritance of traits once again confirms the discreteness of any gene. This property of genes to be the carrier of one hereditary trait is manifested both in the independent combination of alleles of different genes, and in their independent action - in phenotypic expression. The independent distribution of genes can be explained by the behavior of chromosomes during meiosis. During meiosis, pairs of homologous chromosomes, and with them paired genes, are redistributed and diverge into gametes independently of each other.

To verify the correctness of his conclusions, Mendel carried out experiments in which he checked whether the recessive alleles of the gene did not really disappear, but were only masked by the dominant alleles of the gene. Mendel conducted a verification study in all cases of both monohybrid and dihybrid crosses.

Suppose that individuals with genotypes AA and Aa have the same phenotype.

Then, when crossing with an individual that is recessive for this trait and has the aa genotype, the following results are obtained:

In the first case, individuals homozygous for the dominant (AA) gene do not give F1 splitting, and in the other case, heterozygous individuals (Aa) when crossed with a homozygous individual give splitting already in F1.

Similar results were obtained in analyzing (testing) crossing and for two pairs of alleles:

Crossing an individual of an indeterminate genotype with an individual homozygous for recessive alleles is called analyzing cross (Fig. 30). Such crossing is carried out to determine the genotype of an individual. The analysis is not only of theoretical interest, but also of great importance in breeding work.

the first generation of dihybrid crossing (F j). Write them down using the Punnett lattice.

4*. Why are individuals homozygous for dominant alleles not used in analyzing crosses to identify the genotype?

Laboratory work No. 3 (see Appendix c. § 21 Linked inheritance of genes and crossing over At the beginning of the 20th century, when geneticists began to conduct many experiments on crossing on a wide variety of objects (corn, tomatoes, mice, fruit flies, chickens, etc.) , it was found that the patterns established by Mendel are not always manifested. For example, dominance is observed in not all pairs of alleles. Instead, intermediate genotypes arise in which both alleles participate. Many pairs of genes are also found that do not obey the law of independent inheritance of genes, especially if a pair allelic genes are located on the same chromosome, that is, the genes are, as it were, linked to each other.

Such genes are called linked.

The mechanism of inheritance of linked genes, as well as the location of some linked genes, was established by the American geneticist and embryologist T. Morgan. He showed that the law of independent inheritance formulated by Mendel is valid only in cases where genes carrying independent traits are localized on different non-homologous chromosomes. If the genes are on the same chromosome, then the inheritance of traits occurs jointly, i.e.

linked. This phenomenon came to be called linked inheritance, as well as the law of linkage or Morgan's law.

The law of linkage states that linked genes located on the same chromosome are inherited together (linked).

There are many known examples of linked inheritance of genes. For example, in corn, the color of seeds and the nature of their surface (smooth or wrinkled), linked to each other, are inherited together. In the sweet pea (Lathyrus odoratus), flower color and pollen shape are inherited in a linked fashion.

All genes of one chromosome form a single complex - a linkage group.

They usually fall into one sex cell - the gamete and are inherited together.

Therefore, the genes included in the linkage group do not obey Mendel's third law of independent inheritance. However, complete linkage of genes is rare. If the genes are located close to each other, then the probability of chromosome crossing is small and they can remain on the same chromosome for a long time, and therefore will be inherited together. If the distance between two genes on a chromosome is large, then there is a high probability that they can disperse along different homologous chromosomes. In this case, the genes obey the law of independent inheritance.

Thus, Mendel's third law reflects a frequent, but not absolute, phenomenon in the inheritance of traits.

The main evidence for the transmission of heredity was obtained in the experiments of Morgan and his collaborators.

In his experiments, Morgan preferred the fruit fly Drosophila (Drosophila melanogaster). And so far it is a favorite object of research of geneticists. Drosophila can be very easily and quickly bred in the laboratory, and most importantly, it is very convenient for hybridological analysis due to the many elementary traits that are easily taken into account. At present, its genotype has been deciphered, detailed maps of gene linkage groups in chromosomes have been created (Drosophila has only 4 pairs of chromosomes). Many provisions of the chromosome theory of heredity and the properties of the gene were determined by T. Morgan on the basis of experiments with Drosophila. T. Morgan is considered the creator of the chromosome theory of heredity.

Crossing over. Morgan, in studying the inheritance of sex-linked traits, discovered the linear arrangement of genes on a chromosome, formulated the doctrine of the gene as an elementary carrier of hereditary information, and developed a method for constructing genetic maps of chromosomes. He also installed genetic role meiosis and discovered the phenomenon of crossing over. Crossing over was first discovered in the study of the linked inheritance of traits caused by genes located on the same chromosome. During the experiments, a small number of individuals with recombined traits appeared.

In this case, one of the previously linked genes turned out to be in one chromosome, and the second - in another, homologous one, since the chromosomes overlapped and exchanged their sections. This phenomenon was called crossing over (see Fig. 24).

Recall that crossing over occurs at the end of prophase I of meiosis. In the process of meiosis, homologous chromosomes, before dispersing into different nuclei, line up against each other, conjugate (connect), intersect, exchange sites. The farther apart genes are located on a chromosome, the more likely their “separation” during crossing over. The closer to each other their place on the chromosome, the stronger they are linked. As a result of the break and connection in a new order of DNA strands in homologous chromosomes, their sections are mutually exchanged. Previously linked genes may be separated, and vice versa. As a result, new combinations of alleles of different genes are created, allelic genes are rearranged, and new genotypes appear.

Crossing over can occur on any chromosome. The genes that are part of the linkage groups in the chromosomes of the parent individuals, as a result of crossing over, are separated, form new combinations, and in such a new form enter the gametes.

The offspring from such gametes have a new combination of allelic genes, which is the source of the genetic variability observed in populations.

Crossing over is an important source of the emergence of new combinations of genes in the genotypes of individuals and the emergence of trait variability.

Crossing over plays an important role in evolution, as it contributes to the emergence of hereditary variability. By recombining genes, it creates the possibility of selecting individual genes, rather than their combinations. For example, genes that are both beneficial and harmful to the body can be present on the chromosome at the same time. Thanks to crossover, new rearrangements of genes, then subjected to selection, can lead to the disappearance of harmful genes and the preservation of beneficial ones, which will provide an advantage for the existence of an individual with such a genotype in the environment. New genotypes that have arisen as a result of crossing over, in combination with the action of natural selection, can give a new direction in the manifestation of the properties of living organisms, providing them with greater adaptability to environmental conditions.

1. Formulate Morgan's law.

2*. How does crossing over disrupt gene linkage?

3*. Remove the extra word that distorts the correctness of the statement, and complete the statement with the right word.

Linked are genes that lie in the same genotype.

4. Replace the highlighted words with the term.

The source of the emergence of new combinations in the genotypes of individuals ensures the emergence of hereditary variability.

§ 22 Interaction of genes and their multiple action A gene is a structural unit of hereditary information. Materially, a gene is represented by a section of a DNA molecule (in rare cases, RNA). Genes control elementary signs in the process of individual development of the organism. The first studies of the nature of the gene, carried out at the beginning of the 20th century, were mainly aimed at elucidating the role of the gene in the transmission of hereditary traits. An equally important task was to decipher the patterns of action of genes. Its solution has not only theoretical, but also practical significance, since it will prevent possible harmful effects this action.

Genetic studies have established the discrete nature of genes, which is confirmed by their independent inheritance: each of the genes determines the development of some trait independent of the others. However, there are different types of interaction between different genes, due to complex relationships between both allelic and non-allelic genes.

Combining in the genotype, they all together act as a system of interacting individual genes.

Among the interactions of genes, one should first of all name the relations of dominance and recessiveness, when the recessive allele of the gene under the influence of the dominant allele does not appear in the phenotype. In addition, there are facts showing that genes influence the manifestation of the actions of other, non-allelic genes. Cases are also described when the development of one or another trait of an organism is controlled by not one, but many genes. For example, in humans, at least four genes determine the difference in skin color between representatives of the Negroid and Caucasian races.

Among people, occasionally (1:20,000-1:40,000) there are albinos (lat. a / bus - “white”): they have white hair, very fair skin, pink or light blue irises. These people are homozygous for the recessive gene a, the dominant allele of which is responsible for the production of melanin pigment in the body. With the help of melanin, the skin, hair and eyes of a person acquire color. Therefore, the dominant allele A of this gene is often called the normal pigmentation gene. But it turns out that in humans, the synthesis and distribution of melanin depend on a number of other genes located in other loci.

In some people, the dominant F gene causes patchy accumulation of melanin, resulting in freckles, while another dominant P gene causes pigmentation disorders, leaving large areas of the skin light, unpigmented. A number of genes located at other loci affect the amount of melanin in the human body, providing different shades of skin, hair and eye color.

There are many examples showing that the degree of development of the same trait is due to the influence of a number of genes that manifest themselves in a similar way. Different non-allelic genes, as it were, duplicate each other's actions in the manifestation this feature. These interactions of genes are called polymeria (Greek polymereia - “polysyllabicity”), and the genes themselves are called polymeric.

According to the type of polymer, human skin color, plant height, the amount of protein in the endosperm of seeds, the content of vitamins in fruits, the sugar content in sugar beet roots, the rate of biochemical reactions in cells, the growth rate and weight of animals, the egg production of chickens, the milkiness of cows and other important and useful signs of the body.

The phenotypic traits of an organism are usually determined by the interaction of many allelic and non-allelic genes acting in the same direction. However, it is not uncommon for the same gene to cause several traits. This phenomenon is called multiple gene action.

In a horticultural plant, the hybrid gene responsible for the red color of the flower simultaneously determines the purple hue of the leaves, the elongation of the stem, and the large weight of the seeds. In all flowering plants, the genes that provide red (anthocyanin) flower coloration simultaneously control the red color of the stem in the shoot. In the fruit fly Drosophila, a gene that determines the lack of pigment in the eyes affects the color of some internal organs, causes a decrease in fertility and reduces the life expectancy of an individual. In West Pakistan, carriers of the same gene were found, which determine the absence of both sweat glands in certain parts of the body and some teeth.

Polymerism, as well as the multiple action of one gene and its alleles, indicate that the relationship between genes and the manifestation of traits is quite complex. They depend on the combination of allelic and non-allelic genes, and on their location in chromosomes, and on their behavior in mutations, and on many other factors. Therefore, the expression "a gene determines the manifestation of a trait"

quite conditional.

The manifestation of a trait and the very action of a gene always depend on other genes - on the entire genotype, i.e., the genotypic environment.

The concept of genotypic environment was introduced into science by the domestic scientist S.S.

Chetverikov in 1926 to designate a complex of genes that affect the embodiment in the phenotype of a particular gene or group of genes. The genotypic environment is the entire genotype against which the genes act. Moreover, each gene will be realized differently depending on the genotypic environment in which it is located.

Considering the action of a gene, its alleles, it is necessary to take into account not only the genotypic environment that affects the interaction of genes, but also the impact of the environment in which the organism develops.

The degree of manifestation of the trait, i.e., its quantitative characteristics, depends on the external environment. For example, Drosophila, homozygous for the recessive allele, has small (rudimentary) wings in the phenotype. More contrast (more pronounced) this feature is manifested if this fly developed at a low temperature. This example shows that the manifestation of a trait (phenotype) is the result of the interaction of genes in the specific conditions of the existence of an organism.

All signs of an organism (phenotype) develop in the process of interaction between the genotype and the environment.

Only with the simultaneous simultaneous influence of heredity (genotype) and the environment, the signs of the organism (phenotype) appear. The ability of the genotype to be realized in a special way (in different ways) in various environmental conditions and to respond to changing conditions provides the organism with the opportunity to exist in the environment, its viability and development.

1. How does the interaction of genes differ from their multiple action?

2*. Explain the concepts of "genotypic environment" and "external environment".

3. Replace the highlighted words with the term.

The interactions of genes, as well as their ambiguous actions, lead to the conclusion that the relationship between genes and traits is quite complex.

4*. Complete the sentence by choosing the correct words.

Duplicate actions of different genes in the manifestation of this trait are called:

§ 23 Sex Determination and Inheritance of Sex-Linked Characters Most of the evidence in favor of Morgan's chromosome theory of heredity comes from experiments with Drosophila. Careful cytological examination of the cells of this fly helped to detect differences between the chromosomes of males and females. This discovery provided the basis for solving an important question: what mechanisms determine the sex of individuals, i.e., their most profound differences that affect the development of many features and organs directly related to sexual reproduction?

It turned out that Drosophila cells have four pairs of chromosomes. Of these, three pairs are the same for both sexes, and the fourth pair is made up of chromosomes that differ in appearance. Females in the fourth pair have two straight chromosomes, while males have one straight and one curved. Straight chromosomes are called X-chromosomes (X-chromosomes), and curved - Y-chromosomes (Y-chromosomes). A pair of different chromosomes that are not the same in males and females are called sex chromosomes (X and Y). All identical in appearance chromosomes in the cells of dioecious organisms, except for sex chromosomes, are called autosomes (from the Greek autos - “self” and soma - “body”) or non-sex chromosomes (A). The appearance of the chromosomes of the male and female Drosophila is shown in Figure 31. The total number, size and shape of chromosomes characteristic of a particular type of organism is called a karyotype (from the Greek karyon - “core” and typos - “shape”, “sample”) .

All eggs (female gametes) of Drosophila in the haploid set (in the genome) contain four chromosomes, of which one is the X chromosome. Spermatozoa (male gametes) also have four chromosomes, but among them, one half of the spermatozoa carry the X chromosome, and the other half the Y chromosome.

Fertilization of any egg by an X-chromosome containing sperm gives rise to a zygote female type XX. But if the egg is fertilized by a sperm containing a Y chromosome, then a zygote appears male type XY (Fig. 32).

A similar way of determining sex is inherent in all mammals, including humans.

The sex of the offspring is determined by the type of sperm that fertilizes the egg.

Numerous studies of plant, animal and human cells have confirmed the presence of male and female sex chromosomes.

There are 46 chromosomes in all somatic cells (cells of the body). In women, they are represented by 22 pairs of autosomes (non-sex) and a pair of sex chromosomes XX, while in men they are 22 pairs of autosomes and a pair of sex chromosomes XY (Fig. 33).

Like all organisms, in humans, germ cells (egg and sperm) have a haploid set of chromosomes, formed in the process of reduction division in meiosis. Therefore, each egg has 22 autosomes and one X chromosome. Spermatozoa also have a haploid set of chromosomes, but one half of the spermatozoa in a cell, in addition to 22 autosomes, has one X chromosome, and the other half has 22 autosomes and one Y chromosome.

During fertilization, after penetration of a sperm cell with a Y chromosome into the egg, a zygote (X Y) is formed, from which a boy develops, and if a sperm cell with an X chromosome penetrates, then a girl develops from such a zygote (XX). Chromosomes X and Y set the beginning of the whole chain of events that will lead to the suppression of the signs of one and the manifestation of signs of the other sex.

The sex of a person is controlled genetically - by the genes of the sex X and Y chromosomes.

A female (XX) always has one X chromosome from her father and one X chromosome from her mother. A male (X Y) has an X chromosome only from his mother. This is due to the peculiarity of the inheritance of genes located on the sex chromosomes. In humans, the Y chromosome plays a decisive role in sex determination.

Each person inherits from his parents body shape, blood type, skin and eye color, biochemical activity of cells and much more. At the same time, the heredity of a person, like all other organisms, in the manifestation of signs largely follows Mendelian laws. Examples of the inheritance of some human traits are shown in Table 1.

The fact that children are similar to their parents in one way or another indicates the hereditary conditionality of such characteristics.

The distribution of parental traits in the offspring depends on the distribution of parental chromosomes in meiosis and their subsequent pairing in the zygote during fertilization. Sex chromosomes contain genes that determine not only sex, but also other signs of the body, which are called sex-linked.

Inheritance of some human traits The transmission of genes located on the sex chromosomes, and the inheritance of traits controlled by these genes, is called sex-linked inheritance.

The sex chromosomes may contain genes that are not related to sexual characteristics. There are especially many of these genes on the X chromosome. Compared to it, the Y chromosome is genetically inert. Most of the genes on the X chromosome are not present on the Y chromosome. Therefore, the inheritance of traits linked to the sex of an individual can be presented differently in men and women, in females and males in the animal world.

For example, tortoiseshell cats (alternating black and red spots) are found only in females. This fact could not be explained for a long time, until it became known that the B gene - black color and the b gene - red color are located on the X chromosomes. These genes are absent on the Y chromosome. Since the male individual has only one X-chromosome, the cat can be either black or red, but will not have a tortoise color, because its development requires the simultaneous presence in the body of both genes - B and b.

Let us denote the X chromosome carrying the dominant gene B as XB, and the X chromosome with the recessive gene b as Xb. According to the laws of inheritance, the following combinations of pairs of genes in chromosomes and their phenotypes are possible: XB XB - black cat; Xb X b - red cat; Xb X b - tortoiseshell cat; X B Y - black cat; Xb Y - red cat.

There are three types of sex-linked inheritance: inheritance with the help of genes localized on the X chromosome; inheritance due to the presence of alleles of the same genes in the X and Y chromosomes; inheritance observed in the presence of certain genes only on the Y chromosome.

The study of sex-linked inheritance and the mechanism of trait transmission is very important for increasing the viability of living organisms, for the work of breeders, and also for elucidating the causes of hereditary diseases caused by changes in the hereditary material of the organism.

1. How to determine the sex of the future organism?

2*. Build the correct statement.

The total number, size and shape of chromosomes of any kind of living organisms is called:

a) genotype;

b) X-chromosome;

c) Y-chromosome;

d) karyotype.

3*. Include the missing word in the statement.

All identical in appearance chromosomes in the cells of dioecious organisms, except ..., are called autosomes.

4. How many chromosomes are in human cells?

§ 24 Hereditary variability In nature, it is difficult to find two absolutely identical individuals, even in the offspring of the same pair of parents. As you already know, the property of organisms to exist in different forms or states is called variability.

Variability is a common property of all organisms. It manifests itself in them in a number of ways. For example, even two plants of the same species growing side by side differ in the number of shoots and fruits, leaf sizes, and other properties. However, it is not always possible to determine by simple observations whether the variability is the result of a genotype disorder (hereditary) or it is not caused by a genotype disorder. This can only be established by experiment (for example, by crossing).

Any trait is a visible result of the implementation of heredity (genotype) under given conditions. Therefore, the signs depend, on the one hand, on the genetic characteristics of the organism, and on the other hand, on the conditions of his life.

Consequently, variability reflects the relationship of an organism with the environment and affects any of its signs and genetic structures: genes, chromosomes and the genotype as a whole.

The environment continuously affects the body, changing, weakening or enhancing the manifestation of its hereditary characteristics. At the same time, in the process of reproduction, the initial organisms always produce offspring similar to themselves, realizing the continuity of life according to the principle "cell - from cell", i.e.

"Like begets like." The offspring of a pair of cats are always cats, just as the offspring of the single-celled algae chlorella will always be chlorella. By inheriting the properties of the parents, the resemblance to them is transmitted to the offspring.

However, offspring inherit only the genetic material concentrated in the chromosomes. Therefore, children do not inherit traits and properties from their parents, but the genes that control these traits and properties. Moreover, the genes themselves (and chromosomes) in the process of meiosis and the life of an individual undergo a number of changes that are due to:

the action of linked inheritance of traits, as well as sex-linked inheritance; localization of genes in chromosomes; dominance of allelic genes, etc.

This leads to the fact that the offspring have properties that were not in the parents and their ancestors. The variability that has arisen in this way ensures the dissimilarity of descendants and parents.

The variability that appears in connection with a change in the genetic material is called hereditary or genotypic.

One of the results of hereditary variability is the formation of new organisms (new genotypes), which ensures the diversity of life, its continuation and evolutionary development.

Genotypic variability is widely represented in nature. Sometimes these are very large changes, manifested, for example, in signs of doubleness in flowers, short legs in animals (in sheep, chickens), but more often these are small, barely noticeable deviations from the norm.

A change in the genotype usually leads to a change in the phenotype.

Genotypic (hereditary) variability is usually based on new combinations of alleles formed during meiosis, fertilization, or mutation. Therefore, hereditary (genotypic) variability is divided into two types: combinative and mutational. In both cases, the structure of the gene and the structure of chromosomes are disturbed, i.e., the sequence of nucleotides in DNA changes, the number of chromosomes, and the splitting of pairs of alleles of genes occurs; in other words, the genotype changes. All this leads to the emergence of new inherited traits.

Combinative variability is the result of the redistribution of the hereditary material of parents among their offspring. Recombination, or recombination, of genes and chromosomes usually occurs during meiosis (during the process of crossing over, when homologous chromosomes separate) and during fertilization.

Combinative hereditary variability is universal property mutational changes in the shape of the wings, body color, eyes, as well as many physiological signs(life expectancy, fertility, resistance to damaging factors, etc.).

Most mutations are neutral, but there are mutations that are harmful to the organism, some (lethal) even cause its death. Very rarely, mutations useful for the organism occur that improve some properties of an individual, but it is they, fixed in the offspring, that give it some advantages in natural selection over others.

Genotypic variability is inherent in all living organisms. It is the main source of genetic diversity of individuals within a species, which determines the evolution of species in nature and selection. the best forms in the selection.

An important pattern of hereditary variability was revealed by an outstanding domestic scientist - a botanist, geneticist and breeder, N.I. Vavilov. He found that hereditary changes in one species can predict similar changes in similar species and even genera.

The regularity discovered by him is called the law of homological series in hereditary variability or Vavilov's law.

Studying the variability of characters in numerous species and genera of the family of cereals, Vavilov found that in closely related species and genera of cereals, the process of hereditary variability proceeds in parallel and is accompanied by the appearance of similar characters with such accuracy that, knowing a number of forms in one species, it is possible to predict the appearance of similar forms and in other related species and genera.

This pattern was also well traced in legumes, pumpkin, nightshade, cruciferous and other species. It turned out that similar series of hereditary variability are also found at the level of related families (Table 2).

Variability of hereditary traits in representatives of the legume family Hereditary traits Flower color:

purple N.I. Vavilov wrote: "Entire families of plants are generally characterized by a certain cycle of variability passing through all the genera that make up the family."

The theoretical basis for establishing series of trait variability is the idea of the unity of origin of related species from common ancestors who possessed a certain set of genes that appear (or should appear) in descendants in different genera and species. Vavilov's research dealt directly with plants, but the law of homological series of hereditary variability he formulated turned out to be applicable to animals as well.

1. Name the cause of hereditary variability.

2*. Explain the role of genotypic variability in wildlife.

3. In each line, three terms are interconnected in a certain way. Give their general characteristics and define a fourth term that has nothing to do with them.

a) Gene, variability, genotype, heredity.

b) Phenotype, trait, gene, mutation.

c) Combinative variability, mutagen, mutation, genotypic variability.

§ 25 Other types of variability According to the mechanisms of occurrence and the nature of changes in traits, in addition to hereditary (genotypic), two more types of variability are distinguished - modification and ontogenetic.

modification variability. The variability that occurs without changes in the genotype is called modification (from Latin modus- “measure”, “kind” and facio- “I do”), or non-hereditary (phenotypic).

Modification variability is manifested in modifications - changes in the characteristics of an organism (its phenotype) under the influence of environmental factors.

It is not associated with a change in the genotype, but is determined by it. External influences can cause changes in an individual that can be harmful, indifferent or beneficial for it - adaptive adaptations (Latin adaptatio - “adaptation”, “adaptation”). However, all modifications are relative in nature, they act only under specific conditions and are not preserved in other conditions, since they are not fixed in the genotype and are not inherited.

Modifications appear throughout the life of the organism, allowing it to exist in specific environmental conditions.

Modification adaptations are not inherited.

Any pair of organisms of the same species is always somewhat different from each other. In a forest, at the edge, in a forest clearing or in a field nearby, growing plants of the same species differ from each other (in size, growth rate, shape of the crown, inflorescences, etc.), because they develop in unequal environmental conditions: they receive an unequal amount of light, water , minerals, are in contact with the different composition of neighboring species. The same picture is typical for individuals of fungi, animals and all other organisms.

Even the leaves of the same plant have different anatomical, physiological and morphological properties. For example, in lilacs on the sunny side of the bush, the leaves have a light structure, and in the depths of the crown and on the shady side they have a shadow structure (Fig. 34). In vallisneria, arrowhead, water buttercup and many other aquatic plants, the leaves that are under water and above water have different appearance and the internal structure of tissues and cells (Fig. 35).

There are many examples of modification variability. They show that even organisms with the same genotype, but grown in different conditions always differ among themselves in the manifestation of signs, i.e., phenotypically. Such traits are not inherited, since they are not fixed in the genotype.

The modifications observed in Bonellia greena, or the change in the shape of the leaves in arrowhead, lilac, as well as the increase in milk yield when the cows are abundantly fed, the increased branching of the shoots when pruning the apical buds, the improvement in health with the use of vitamins, and many similar examples of a quantitative nature, appear in a similar way. in all individuals of each species. Therefore, modification variability is also called group (mass) or specific. These terms were introduced by C. Darwin. He noted that a certain variability is observed in cases where all individuals of a given breed, or variety, or species, under the influence of a certain cause, change in the same way in one direction.

reaction rate. Modification variability has rather rigid boundaries, or limits, for the manifestation of a trait, due to the genotypic property of an individual. The limits of the modification variability of an organism's trait are called its reaction norm. The reaction rate characterizes the ability of organisms of a given species to respond (within the genotype) to changing conditions and the possibility of manifestation of signs in certain specific conditions in a special way. Some signs (for example, egg production, milkiness, fat accumulation, weight and growth of organisms), i.e. signs of a quantitative nature, have a very wide reaction rate, others (color of wool, seeds, leaf shape, size and shape of eggs), i.e. .qualitative features - very narrow. The limits of the reaction norm are determined by the genotype.

Domesticated Japanese quail lays eggs, the average weight of which is 10 g.

exposure to UV rays sunburn gradually disappears. In some fish, there is a sex change to the opposite and vice versa, and sometimes this process takes only a few minutes (for example, in seranus perches). In most cases, modifications are unstable and disappear as soon as the action of the factors that caused them ceases, but they give individuals the opportunity to survive in specific changed conditions.

Modifications are non-inherited adaptive reactions of the body (and cells) to changes in environmental conditions.

The basis of modification variability is the phenotype as a result of the interaction of the genotype and external conditions. Therefore, this type of variability is also called phenotypic.

The significance of modification variability was well expressed by the domestic scientist who studied the issues of evolution, I.I. Schmalhausen: "Adaptive (adaptive) modification is the first test of the reaction, with the help of which the body, as it were, checks the possibility of replacing and more successfully using the environment."

The role of modification variability in nature is great, since it provides organisms with the opportunity to adapt (adapt) to changing environmental conditions during their ontogenesis.

ontogenetic variability. Ontogenetic, or age-related, variability is called the regular changes in the body that occurred in the course of its individual development (ontogenesis). With such variability, the genotype remains unchanged, therefore it is classified as non-hereditary. However, all ontogenetic changes are predetermined by hereditary properties (genotype), which often change during ontogenesis. As a result, new properties appear in the genotype. This brings ontogenetic variability closer to hereditary. Thus, ontogenetic variability occupies an intermediate position between hereditary and nonhereditary variability (Table 3).

Types of variability All types of variability are of great importance in the life of organisms.

Variability, i.e., the ability of organisms to exist in different variations, in the form of individuals with different properties, - one of critical factors life, ensuring the adaptability of organisms (populations and species) to changing conditions of existence and causing the evolution of species.

1. Is it possible, by improving the feeding conditions, to turn short-haired cats into long-haired ones?

2*. Explain the role of the reaction norm in the life of an individual and a species. 3. In each line, three terms are interconnected in a certain way. Give their general characteristics and define a fourth term that has nothing to do with them.

Modification, phenotypic, mutational, definite (variability).

Ontogenetic, hereditary, non-hereditary, adaptive (variability).

Laboratory work No. 4 (see Appendix, p. 231).

§ 26 Sex-linked hereditary diseases There are about 3,000 hereditary diseases and anomalies (malformations) in medical genetics. The study and possible prevention of the consequences of human genetic defects are of great importance for its conservation as a species. Currently, about 4% of newborns suffer from genetic defects. It is believed that about one in 10 human gametes carries erroneous information due to a mutation. Gametes with errors in the genetic material cause miscarriages or stillbirths.

All hereditary diseases can be divided into two large groups:

diseases associated with gene mutations; and diseases associated with chromosome mutations.

Genetic diseases and anomalies. These include pathological conditions organisms that result from a mutation in a gene. For example, a violation of DNA replication leads to a change in the alternation of nucleotide pairs, which, in turn, causes "errors" in metabolism.

Many congenital (with which an individual is born into the world) anomalies and diseases are caused by disorders in genes located on the X or Y chromosome. In these cases, one speaks of sex-linked inheritance. For example, such an anomaly as color blindness (the inability to distinguish between red and green colors) is caused by a gene located on the X chromosome.

In humans, one of the genes on the X chromosome is responsible for color vision. The recessive allele does not provide for the development of the retina, which is necessary to distinguish between red and green colors. A man who carries such a recessive gene on his X chromosome suffers from color blindness, that is, he distinguishes between yellow and blue colors, but green and red seem the same to him. Color blindness is not transmitted through the male line, since color blind men receive their X chromosome from a mother who carries a defective gene (Fig. 37). A woman can only be colorblind if her father is colorblind and her mother is a carrier of this recessive gene.

Sex-linked (genes are located on the X chromosome) are also inherited Various types hemophilia, in which the blood does not clot and a person can die from blood loss even with a small scratch or cut.

This disease occurs in men whose mothers, being healthy, are carriers of the recessive hemophilia gene.

It has been established that hemophilia is caused by a recessive gene located /v on the X chromosome, therefore, women heterozygous for this gene have normal blood clotting. Married to a healthy man (not a hemophilic! A woman passes on half of her sons an X chromosome with a gene for normal blood clotting, and half an X chromosome with a hemophilia gene. Moreover, daughters have normal blood clotting, but half of them may be carriers of the hemophilia gene, which will affect the male offspring in the future.

The distribution of hemophilia by inheritance is well studied among descendants. royal families Europe. The distribution scheme of hemophilia in these families is shown in Figure 38.

Chromosomal diseases. This type of hereditary disease is associated with changes in the number or structure of chromosomes. In most cases, these changes are not transmitted from diseased parents, but occur when there is a violation in the divergence of chromosomes during meiosis, when gametes are formed, or when mitosis is disturbed in the zygote at different stages of crushing.

Of the chromosomal (autosomal) diseases, Down's disease has been studied in the most detail. This disease is associated with nondisjunction during the division of the 21st chromosome. As a result of such an anomaly, embryonic cells have 47 chromosomes instead of the usual 46 for humans. Chromosome-21 is not in double, but in triple quantity (trisomy).

Typical signs of patients with Down syndrome are a wide bridge of the nose, slanting eyes with a special crease of the eyelid, an always open mouth with a large tongue, and mental retardation. About half of them have heart defects. Down's disease is quite common. However, in young mothers (under 25) such children are rarely born (0.03-0.04% of newborns), and in women over 40, almost 2% of children are born with Down syndrome.

FEDERAL FOREST AGENCY OF THE RUSSIAN FEDERATION ULYANOVSK BRANCH OF FSUE ROSLESINFORG FOREST REGULATION OF THE RADISCHEVSKOYE FORESTRY OF THE MINISTRY OF FORESTRY, NATURE MANAGEMENT AND ECOLOGY OF THE ULYANOVSK REGION Director R.M. Gareev Chief Engineer N.I. Starkov Ulyanovsk 2012 3 CONTENTS No. Section Page title Introduction Chapter 1 General information Brief description of forestry 1.1. Distribution of the territory of the forestry by municipal 1.2. formations Location of forestry 1.3....»

Ostroumov S.A. Concepts of ecology ecosystem, biogeocenosis, boundaries of ecosystems: the search for new definitions // Bulletin of Moscow State University. Series 16. Biology. 2003. No. 3. P.43-50. Tab. Res. in English. lang. Bibliography 44 titles [New interpretation, new definition options. The differences between the new definitions and the previously existing ones are listed and substantiated. It is proposed to single out 2 types of uncertainty of the boundaries of the ecosystem (p.46-48). A new concept of a two-zone (double-circuit) spatial structure has been formulated ... "

"D. B. Kazansky, L. A. Pobezinsky, T. S. Tereshchenko MOTIVES IN THE PRIMARY STRUCTURE OF MHC CLASS I MOLECULES AND THEIR USE TO CREATE SYNTHETIC LIGANDS OF CELLULAR RECEPTORS 115478, Kashirskoye shosse, 24 In this work, we attempted to describe the huge variety of allelic forms of molecules of the major histocompatibility complex (MHC) of class I mammals in the form of a single formula, ... "

«self), according to modern authors, a complex neurobiological disorder, a severe mental disorder, an extreme form of self-isolation that occurs as a result of impaired brain development. In 1943, Dr. Leo Kaner of the Johns Hopkins Hospital first described this condition and gave it the name "autism". Almost simultaneously with him, ... "

“Bulletin of MSTU, volume 15, No. 4, 2012, pp. 739-748 UDC 551.46 (268.41) To assess the oceanological knowledge of the Barents and White Seas S.L. Dzhenyuk Murmansk Marine Biological Institute KSC RAS Abstract. A description of the current level of knowledge about oceanological characteristics and indicators of the state of the ecosystems of the Barents and White Seas is given. A methodical approach is proposed to assess the knowledge of the oceanological and hydrobiological regime, based on a statistical description of the studied ... "

“with elements of isotherapy, at primary school age Box + with eve’s gifts Classification of vowel sounds according to place and degree of rise Contest mptur Corpus from bp to against cp Number of people in the Krasnodar Territory with the name tatyana korenyuk Brick red m 100 in Ufa Book biology bilych and Kryzhanovsky Korolev SV The book of a modern gardener / m I Sukhotsky download The design of the sauna with drawings The king and the jester - the Drevlyans remember the battle with bitterness Composition a horse with a pink mane Cork-s overalls Cocktail from ... "

«FEDERAL AGENCY OF FORESTRY OF THE RUSSIAN FEDERATION ULYANOVSK BRANCH OF FSUE ROSLESINFORG FORESTRY REGULATION OF THE SURSKY FORESTRY OF THE MINISTRY OF FORESTRY, NATURE MANAGEMENT AND ECOLOGY OF THE ULYANOVSK REGION Director R.M. Gareev Chief Engineer N.I. Starkov Ulyanovsk 2012 3 CONTENTS № Section Page name Introduction Chapter 1 General information Brief description of the forest area 1.1. Distribution of the territory of the forestry by municipal 1.2. formations Location of forestry 1.3....»

«UDK 581.151+582.28-19(470.5+571.1/.5)+504.5+504.7 A. G. Shiryaev CHANGES IN THE MYCOBIOTA OF THE URAL-SIBERIAN REGION UNDER THE CONDITIONS OF GLOBAL WARMING AND ANTHROPOGENIC IMPACT An analysis of long-term studies of changes in the conditions of the mycobiota in the Ural-Siberian region is undertaken global warming and associated anthropogenic impact. The main trend is the enrichment of its mycobiota with species from other geographical areas, the expansion of the range of a number of southern species to the north ... "

"FHPP for motor controller CMMP-AS-.-M3 Description Profile developed by Festo for handling and positioning systems based on fieldbus: – CANopen – PROFINET – PROFIBUS – EtherNet/IP – DeviceNet – EtherCAT with interface: – CAMC-F-PN – CAMC-PB – CAMC-F-EP – CAMC-DN – CAMC-EC for motor controller CMMP-AS-.-M 1205NH CMMP-AS-.-M Translation of the original operating instructions GDCP-CMMP-M3-C-HP- EN CANopen®, PROFINET®, PROFIBUS®, EtherNet/IP®, STEP 7®, DeviceNet®, EtherCAT®, TwinCAT®,...»

"Ministry of Natural Resources and Environmental Protection of the Republic of Komi State Institution of the Republic of Komi Territorial Fund of Information on Natural Resources and Environmental Protection of the Republic of Komi STATE REPORT ON THE STATE OF THE ENVIRONMENT OF THE REPUBLIC OF KOMI IN 2012 Syktyvkar 2013 STATE REPORT IS 20 YEARS Dear readers! In your hands is the anniversary issue of the State Report on the State of the Environment of the Republic of Komi. The first edition of the report was…”

«FEDERAL AGENCY OF FORESTRY OF THE RUSSIAN FEDERATION FOREST REGULATIONS OF THE SURSKY FORESTRY OF THE MINISTRY OF FORESTRY, NATURE MANAGEMENT AND ECOLOGY OF THE ULYANOVSK REGION Director R.M.Gareev Chief engineer N.I.Starkov Ulyanovsk 2012 Chapter 1 Title. Brief description of the forestry Distribution of the territory of the forestry by municipal 1.2. formations 1.3. Placement of the forestry Distribution of forests of the forestry by ... "

«www.ctege.info C5 The cell as a biological system 2.1. Cell theory, its main provisions, role in the formation of the modern natural-science picture of the world. Development of knowledge about the cell. The cellular structure of organisms, the similarity of the structure of the cells of all organisms - the basis of the unity of the organic world, evidence of the relationship of living nature. We already..."

“G.G. Goncharenko, A.V. Kruk BIOTECHNOLOGY BASICS 3' 5' CG TA GC AT GC TA TA TA CG TA 3' 5' Gomel 2005 MINISTRY OF EDUCATION OF THE REPUBLIC OF BELARUS Institution of Education Gomel State University named after Francis Skorina G.G. Goncharenko, A.V. Kruk FUNDAMENTALS OF BIOTECHNOLOGY Texts of lectures for students of the specialty I - 31 01 01 - Biology (scientific and pedagogical activity) Gomel UDC 60 (075.8) BBK 30. 16 Ya G Reviewers: L.I. Korochkin, corresponding member. RAS, Doctor of Medical Sciences B.A...."

"Ministry of Health and Social Development of the Russian Federation FGU Scientific Center for Obstetrics, Gynecology and Perinatology named after A.I. IN AND. Kulakova Russian Society of Obstetricians and Gynecologists Association for Cervical Pathology and Colposcopy Russian Society for Contraception Congress Operator CJSC MEDI Expo All-Russian Congress Ambulatory Polyclinic Practice – New Horizons Collection of Abstracts Moscow March 29 – April 2, 2010. All-Russian Congress Outpatient practice - new horizons...»

« graduate in the direction 656600 Environmental protection specialty 280201 Environmental protection and rational use of natural resources full-time and part-time forms SYKTYVKAR 2007 FEDERAL AGENCY FOR EDUCATION SYKTYVKAR FOREST INSTITUTE - BRANCH OF THE STATE EDUCATIONAL INSTITUTION...»

April 2014 COFO/2014/6.3 R COMMITTEE ON FORESTRY TWENTY-SECOND SESSION Rome, Italy, 23-27 June 2014 VOLUNTARY GUIDELINES FOR NATIONAL FOREST MONITORING I. INTRODUCTION Forest monitoring has become a key element of national and 1. international norm-setting processes environmental and development issues. Information provided as part of monitoring activities forest resources, 2. has importance for many international agreements, ... "

«Series PROBLEMS AND CONTRADICTIONS IN NEONATOLOGY GASTROENTEROLOGY AND NUTRITION 978-5-98657-036-5 HEMATOLOGY, IMMUNOLOGY AND INFECTIOUS DISEASES 978-5-98657-037-2 HEMODYNAMICS AND CARDIOLOGY 5-98657-039-6 NEUROLOGY 978-5-98657-041-9 NEPHROLOGY AND WATER AND ELECTROLYTE METABOLISM 978-5-98657-040-2 Gastroenterology and Nutrition Neonatology Questions and Controversies Josef Neu, MD Professor of Pediatrics University of Florida College of Medicine Gainesville, Florida...»

“D.V. Bokhanov, D.L. Laius, A.R. Moiseev, K.M. Sokolov ASSESSMENT OF THE THREATS TO THE MARITIME ECOSYSTEM OF THE ARCTIC ASSOCIATED WITH INDUSTRIAL FISHING BY THE EXAMPLE OF THE BARENTS SEA UDC 574.5 (268.45) LBC 28.082 O-93 D.V. Bokhanov ( World Foundation wildlife) D.L. Laius (St. Petersburg State University) A.R. Moiseev (World Wildlife Fund) K.M. Sokolov (Polar Research Institute of Fisheries and Oceanography) Assessment of threats to the marine ecosystem of the Arctic associated with industrial ... "

«www.ctege.info В8 Section 2 The cell as a biological system 2.1. Cell theory, its main provisions, role in the formation of the modern natural-science picture of the world. Development of knowledge about the cell. The cellular structure of organisms, the similarity of the structure of the cells of all organisms - the basis of the unity of the organic world, evidence of the relationship of living nature. We..."

Prokaryotes. Eukaryotes. cell organelles. Monomers. Polymers. Nucleic acids. DNA. RNA. Enzymes. Biosynthesis. Photosynthesis. Metabolism. Biological oxidation (cellular respiration). Chapter 3

Reproduction and individual development of organisms (ontogenesis)

After studying the chapter, you will be able to:

Describe the two main types of reproduction and their role in the evolution of life;

Tell about the biological significance of fertilization and the role of the zygote;

To reveal the essence of mitosis and meiosis and their meaning;

Explain the processes of cell division and its biological significance;

Describe the stages of ontogeny.

§ 13 Types of reproduction

Reproduction is the reproduction of their own kind, ensuring the continuation of the existence of the species.

Reproduction is the main property of all organisms. As a result of reproduction, the number of individuals of a certain species increases, continuity and succession is carried out in the transfer of hereditary information from parents to offspring. Having reached a certain size and development, the organism reproduces its offspring - new organisms of the same species and settles them in the surrounding space.

The diversity of organisms that has historically developed on Earth has led to an extremely wide variety of methods of reproduction. However, all of them are only variants of the two main types of reproduction - asexual and sexual.

Asexual reproduction is the self-reproduction of organisms, in which only one individual (the parent) participates. In sexual reproduction, as a rule, two individuals (two parents) participate - female and male.

Sexual reproduction. The main feature of sexual reproduction is fertilization, i.e., the fusion of female and male germ cells and the formation of one common cell - a zygote (Greek zygotes - “connected together”). The zygote gives rise to a new organism in which the hereditary properties of the two parent organisms are combined.

Sex cells - gametes (Greek gametes - "spouse") - are formed in parent organisms in special organs. In animals and humans, they are called genitals, in plants - generative organs (Greek genero- “I produce”, “I give birth”). Male and female gametes develop in the reproductive organs of animals and in the generative organs of plants. Male gametes are usually small cells containing only a nuclear (hereditary) substance. Some of them are immobile (sperm), others are mobile (spermatozoa).

Sperms develop in all angiosperms and gymnosperms, and spermatozoa develop in algae, mosses, ferns, and in most animal organisms, including humans.

Female gametes (eggs) are fairly large cells, sometimes a thousand times larger than spermatozoa. In addition to the nuclear substance, the eggs contain a large supply of valuable organic matter necessary after fertilization for the development of the embryo.

Fertilization in many primitive organisms (filamentous green algae, such as spirogyra, some types of bacteria, ciliates, mold fungi, etc.) is carried out by the fusion of two morphologically identical cells, resulting in the formation of one cell - a zygote. Such a sexual process is called conjugation (Latin conjugatio - “connection”). Merging cells are also called gametes. Their conjugation (fusion) gives a zygote.

Two adjacent cells of the same spirogyra filament or cells of two different adjacent filaments can conjugate. In this case, the role of the female reproductive cell is performed by the one into which the contents of another cell flows. The flowing content is considered the male sex cell.

In the ciliate shoe caudate conjugate two identical free-swimming individuals. Moreover, they do not merge the contents of the cells together, but exchange nuclear matter with each other.

Thus, sexual reproduction is characterized by the development of germ cells, fertilization and the formation of a zygote that combines the hereditary substance of two different parental individuals. As a result, each daughter individual developing from a zygote contains new properties - from two different organisms of the same species.

During sexual reproduction, an organism always arises with unique properties that have not yet been found in nature, although very similar to its parents. Such organisms with new hereditary properties obtained from both parents often turn out to be more adapted to life in changing environmental conditions.

During sexual reproduction, there is a constant renewal of hereditary properties in the daughter generations of organisms. This is the greatest biological role of sexual reproduction in the evolution of living things.

There is no such renewal in asexual reproduction, when daughter organisms develop from only one parent and carry only its hereditary properties.

Asexual reproduction. This is ancient way reproduction of their own kind, characteristic of organisms of all kingdoms of wildlife, especially prokaryotes. This method of reproduction, carried out without the participation of germ cells, is widespread in unicellular organisms, in fungi and bacteria.

In unicellular and multicellular organisms, asexual reproduction is carried out by division and budding. Division in prokaryotes occurs by constriction of the cell into two parts. In eukaryotes, division is more complicated and is provided by processes occurring in the nucleus (see § 14).

An example of asexual reproduction is vegetative reproduction in plants. In some animals, vegetative reproduction also occurs. It is called reproduction by fragmentation, that is, parts (fragments) of the body from which a new individual develops. Reproduction by fragments is typical for sponges, coelenterates (hydra), flatworms(planaria), echinoderms (starfish) and some other species.

In unicellular and some multicellular animals, as well as in fungi and plants, asexual reproduction can be carried out by budding. On the mother's body, special outgrowths are formed - kidneys, from which new individuals develop. Another type of asexual reproduction is sporulation. Spores are separate, very small specialized cells that contain a nucleus, cytoplasm, are covered with a dense membrane and are able to endure adverse conditions for a long time. Once in favorable environmental conditions, spores germinate and form a new (daughter) organism. Sporulation is widely represented in plants (algae, bryophytes, ferns), fungi and bacteria. Among animals, sporulation is observed, for example, in sporozoans, in particular in malarial plasmodium.

It is noteworthy that during asexual reproduction, the separated daughter individuals completely reproduce the properties of the mother organism. Once in other environmental conditions, they can manifest their properties differently, mainly only in the size (size) of new organisms. Hereditary properties remain unchanged.

The ability to repeat the unchanged hereditary qualities of the parent in daughter organisms, that is, to reproduce homogeneous offspring, is a unique property of asexual reproduction.

Asexual reproduction allows you to keep the properties of the species unchanged. This is the important biological significance of this type of reproduction. Organisms that appeared asexually usually develop much faster than those that appeared through sexual reproduction. They quickly increase their numbers and much faster carry out resettlement over large areas.

In most unicellular and multicellular organisms, asexual reproduction can alternate with sexual reproduction.

For example, in some marine coelenterates, the sexual generation is represented by single free-swimming jellyfish, and the asexual generation is represented by sessile polyps. In plants, for example, in ferns, the sexual generation (gametophyte) is represented by a small leaf-like outgrowth, and the asexual generation (sporophyte) is a large leafy plant on which spores develop (Fig. 19).

It is characteristic that asexual reproduction occurs when the organism is in favorable conditions for it. When conditions worsen, the organism switches to sexual reproduction. In many highly developed plants and animals, sexual reproduction begins only after the organism has passed through a series of definite stages in its development and has reached the age of sexual maturity.

Asexual and sexual reproduction are the two main ways of continuing life, formed in the process of evolution of wildlife.

1. Explain the evolutionary advantage of sexual reproduction over asexual reproduction.

2*. What is the biological role of asexual reproduction in the evolution of living things?

The fusion of two adjacent, adjacent cells is a method of fertilization in many primitive organisms.

Motile male sex cells develop in most animals and plants, while immobile male sex cells develop only in seed plants.

§ 14 Cell division. Mitosis

All new cells arise by dividing an already existing cell, realizing the basic law of life: "a cell - from a cell." This process is observed in both unicellular and multicellular organisms.

In unicellular organisms, cell division underlies asexual reproduction, leading to an increase in their numbers. In multicellular organisms, division underlies the formation of the organism itself. Having begun their existence with a single cell (zygote), thanks to repeatedly repeated division, they create billions of new cells by asexual reproduction: in this way, the body grows, its tissues are renewed, and aged and dead cells are replaced. Cell division does not stop throughout the life of the organism - from birth to death.

It is known that cells age over time (they accumulate unnecessary metabolic products) and die. It is estimated that in an adult total cells is more than 10 15 . Of these, about 1-2% of cells die daily. So, liver cells live no more than 18 months, erythrocytes - 4 months, epithelial cells of the small intestine - 1-2 days. Only nerve cells live throughout a person's life and function without being replaced. All other human cells are replaced by new ones approximately every 7 years.

All cell replacements in the body are carried out by their constant division.

Self-reproduction by division is a common property of cells of unicellular and multicellular organisms. However, this process occurs differently in prokaryotic and eukaryotic cells.

Cell division in prokaryotes. Cell division of prokaryotes is due to the peculiarities of the structure of their cells. Prokaryotic cells do not have a nucleus or chromosomes. Therefore, cells multiply by simple division. The nuclear substance in bacteria is represented by a single circular DNA molecule, which is conventionally considered a chromosome. DNA is circular in shape and is usually attached to the cell membrane. Before dividing, the bacterial DNA is duplicated, and each of them, in turn, is attached to the cell membrane. Upon completion of DNA duplication, the cell membrane grows between the resulting two DNA molecules. Thus, the cytoplasm is divided into two daughter cells, each of which contains an identical circular DNA molecule (Fig. 20).

Cell division in eukaryotes. In eukaryotic cells, DNA molecules are enclosed in chromosomes. Chromosomes play a major role in the process of cell division. They ensure the transfer of all hereditary information and participation in the regulation of metabolic processes in daughter cells. The distribution of chromosomes between daughter cells and the transfer of a strictly identical set of chromosomes to each of them achieves the continuity of properties in a number of generations of organisms.

When dividing, the nucleus of a eukaryotic cell goes through a series of sequentially and continuously following each other stages. This process is called mitosis (Greek mitos- "thread").

As a result of mitosis, first doubling occurs, and then a uniform distribution of the hereditary material between the two nuclei of the emerging daughter cells.

Depending on what happens in a dividing cell and how these events look under a microscope, there are four phases, or stages, of mitosis, following one after another: the first phase is prophase, the second is metaphase, the third is anaphase and the fourth, final, - telophase. Let us consider what happens in the nucleus at different stages of fission (Fig. 21).

Metaphase. Chromosomes move to the center of the cell. Each of them consists of two chromatids connected by a centromere. One end of the spindle threads is attached to the centromeres.

Anaphase. Microtubules contract, centromeres separate and move away from each other. The chromosomes separate and the chromatids move to opposite poles of the spindle.

Simultaneously with telophase, the division of the cytoplasm begins. First, a constriction (partition) is formed between the daughter cells. After some time, the contents of the cell are divided. This is how new daughter cells appear with cytoplasm around new identical nuclei. After that, the preparation for the division of the now new cell begins again, and the whole cycle is repeated continuously, if there are favorable conditions. The process of mitosis takes about 1-2 hours. Its duration varies in different types of cells and tissues. It also depends on environmental conditions.

The division of the nucleus and, consequently, the cell goes on continuously as long as the cell has the means to ensure its vital activity.

At the second stage of the cell cycle, mitosis occurs and the cell divides into two daughter cells.

After separation, each of the two daughter cells again enters the interphase period. From this moment on, both eukaryotic cells that have arisen begin a new (now their own) cell cycle.

As you can see, cell division in eukaryotes and prokaryotes occurs in different ways. But both simple division in prokaryotes and division by mitosis in eukaryotes are methods of asexual reproduction: daughter cells receive the hereditary information that the parent cell had. Daughter cells are genetically identical to the parent. There are no changes in the genetic apparatus here. Therefore, all cells that appear in the process of cell division and the tissues formed from them have genetic homogeneity.

1. Explain the differences in the processes of cell division in prokaryotes and eukaryotes.

2*. Why are the offspring identical to the parent in asexual reproduction?

3. Describe the process of mitosis and the features of each of its stages.

4. Replace the underlined words with terms.

The first phase of mitosis begins when the chromosomes become visible.

At the end of the third phase of mitosis, the chromosomes are at opposite poles of the cell.

Cell structures containing genetic information become visible only during mitosis.

Laboratory work No. 2 (see Appendix, p. 230).

§ 15 Formation of sex cells. Meiosis

Sex cells (gametes) develop in the genital (generative) organs and play a crucial role: they ensure the transfer of hereditary information from parents to offspring. During sexual reproduction, as a result of fertilization, two germ cells (male and female) merge and form one cell - a zygote, the subsequent division of which leads to the development of a daughter organism.

Usually, the cell nucleus contains two sets of chromosomes - one from one and the other parent - 2p (the Latin letter "p" denotes a single set of chromosomes). Such a cell is called diploid (from the Greek diploos - "double" and eidos - "view"). It can be assumed that when two nuclei merge, the newly formed cell (zygote) will contain not two, but four sets of chromosomes, which will double again with each subsequent appearance of zygotes. Imagine how many chromosomes would then accumulate in one cell! But this does not happen in living nature: the number of chromosomes in each species during sexual reproduction remains constant. This is due to the fact that germ cells are formed by a special division. Due to this, not two (2n), but only one pair of chromosomes (In), that is, half of what was in the cell before its division, enter the nucleus of each germ cell. Cells with a single set of chromosomes, that is, containing only half of each pair of chromosomes, are called haploid (from the Greek haploos - "simple", "single" and eidos - "view").

The process of division of germ cells, as a result of which there are half as many chromosomes in the nucleus, is called meiosis (Greek meiosis - “reduction”). A halving of the number of chromosomes in the nucleus (the so-called reduction) occurs during the formation of both male and female germ cells. During fertilization by fusion of germ cells in the nucleus of the zygote, a double set of chromosomes (2p) is again created.

With the help of meiosis, germ cells are formed with a smaller set of chromosomes and with qualitatively different genetic properties than those of the parent cells.

Meiosis, or reduction division, is a combination of two peculiar stages of cell division, following each other without interruption. They are called meiosis I (first division) and meiosis II (second division). Each stage has several phases. The names of the phases are the same as the phases of mitosis. Interphases are observed before divisions. But doubling of DNA in mitosis occurs only before the first division. The course of meiosis is shown in Figure 23.

In the first interphase (preceding the first division of meiosis), there is an increase in cell size, doubling of organelles and doubling of DNA in chromosomes.

Due to crossing over, chromosomes with other hereditary properties in comparison with the chromosomes of parental gametes turn out to be in germ cells.

The phenomenon of crossing over is of fundamental biological importance, as it increases the genetic diversity in the offspring.

The complexity of the processes occurring in prophase I (in chromosomes, nucleus) determines the longest duration of this stage of meiosis.

Telophase I is followed by a second interphase. It takes a very short time, since DNA synthesis does not occur in it.

The second division (meiosis II) begins with prophase II. Two daughter cells that have arisen in telophase I begin division similar to mitosis: the nucleoli and nuclear membranes are destroyed, spindle filaments appear, with one end attached to the centromere. In metaphase, the chromosomes line up along the equator of the spindle. In anaphase II, the centromeres divide, and the chromatids of the chromosomes in both daughter cells diverge towards their poles.

As a result, from each duplicated chromosome, two separate chromosomes are obtained, which move to opposite poles of the cell. At both poles, a nucleus is formed from groups of chromosomes gathered here. In it, each pair of homologous chromosomes is represented by only one chromosome.

As a result of meiosis, four cells with a haploid set of chromosomes appear from one cell.

1. Why are the properties of the daughter organisms that developed from the zygote not identical to those of the parent?

2*. What is the biological meaning of meiosis?

3. Replace the highlighted words with the term.

Cell division, as a result of which there are half as many chromosomes in the nucleus, leads to the formation of germ cells.

4. Complete the statement by choosing the correct term:

The same chromosomes from father and mother are called:

a) haploid; c) diploid;

b) homologous; d) single.

§ 16 Individual development of organisms - ontogenesis

The body undergoes significant transformations during the period of its life: it grows and develops.

Unicellular organisms, like all cells, arise by cell division. In a newly formed cell, intracellular structures are not always formed that provide its specific functions and life processes. It takes a certain time for all organelles to form and all the necessary enzymes to be synthesized. This early period of existence of a cell (and a single-celled organism) in the cell cycle is called maturation. It is followed by a period of mature cell life, culminating in its division.

In the vast majority of animal organisms, the process of embryonic development occurs in a similar way. This confirms the commonality of their origin.

The lion dies of old age at the age of about 50, the crocodile can live up to 100 years, the oak - up to 2000 years, the sequoia - more than 3000 years, and the oats - 4-6 months. Some insects live for several days. A person dies of old age between the ages of 75-100, although some people live to be over 100 years old.

Postembryonic development consists of three age periods: youth, maturity and old age. Each of these periods is characterized by certain transformations in the structure and life processes of the organism, due to its heredity and the influence of external conditions. In the process of postembryonic development, the organism undergoes quantitative and qualitative changes.

Ontogenesis is the development of an individual (individual) due to heredity and the influence of environmental conditions.

Ontogeny is certainly one of the most amazing biological phenomena. Having appeared in the form of a tiny embryo or germ, the body goes through a number of complex stages of development, during which all the organs and mechanisms that ensure vital activity are gradually formed in it. Having reached puberty, the organism realizes the main function of the living - it gives offspring, which ensures the duration and continuity of the existence of its species.

The existence of any organism is a complex and continuous process of embryonic and postembryonic development in certain habitat conditions and over the periods characteristic of each species.

1. Describe the period of embryonic development of the organism.

2. Replace the terms with the following definitions: an organism in the early stages of development; individual development of a multicellular organism.

3*. Explain why the influence of dangerous external influences (radiation, smoking) is more destructive at the embryonic stage of ontogenesis than at the postembryonic stage.

Reproduction is inherent in all living organisms. With the help of reproduction, self-reproduction of organisms and the continuity of the existence of the species are ensured. There are two main types of reproduction in organisms - asexual and sexual. Indirect cell division (mitosis) during the passage of a series of phases (prophase, metaphase, anaphase, telophase) ensures the transfer to daughter cells of the same hereditary information contained in the chromosomes of the nucleus as the parent. Interphase prepares the cell for division.

Sexual reproduction arose in the process of evolution later than asexual. Through meiosis, crossing over, and fertilization, sexual reproduction provides genetic variability that allows organisms to acquire new traits and properties, and thus better adapt to changing environmental conditions.

In the process of meiosis, the reduction division of germ cells and the formation of a haploid (In) set of chromosomes in the nucleus of gametes occur. When cells are fertilized, the male and female germ cells merge with a haploid set of chromosomes and a zygote is formed with a diploid (2p) set of chromosomes in the nucleus.

The individual development of all organisms is carried out in accordance with the hereditary properties inherent in the species, and depending on the environmental conditions.

Test yourself

1. Explain how the biological role of female and male sex gametes is manifested.

2. Explain the main differences between mitosis and meiosis.

3. What is the dependence of the individual development of the organism on environmental conditions in the embryonic and postembryonic periods?

4. What stages are observed in the cell cycle of unicellular organisms? Explain the importance of interphase in the life of a cell.

1. Describe the concepts of "growth of the organism" and "development of the organism."

Issues for discussion

1. Describe the biological role of different types of reproduction if they are observed in organisms of the same species. Give examples.

2. Expand the mechanism for ensuring the continuity of life.

Basic concepts

Asexual reproduction. Sexual reproduction. Gamete. Zygote. Chromosome. Mitosis. Meiosis. Crossing over. Cell cycle. diploid cell. haploid cell. Ontogenesis.

Fundamentals of the doctrine of heredity and variability

After studying the chapter, you will be able to:

Explain the basic concepts of genetics;

Describe the mechanism of sex determination and types of trait inheritance;

Describe the role of heredity and variability of organisms in wildlife.

§ 17 From the history of the development of genetics

Genetics (Greek genesis - “origin”) is the name of the science that studies the heredity and variability of organisms, as well as the mechanisms for controlling these processes. It has a long history.

However, only in the 19th and early 20th centuries, when knowledge about the life of the cell was accumulated, scientists began to study the phenomenon of heredity. The first scientific work on the study of heredity was carried out by the Czech scientist and monk G. Mendel. In 1865, in the article "Experiments on plant hybrids," he formulated the patterns of inheritance of traits that laid the foundation for the science of genetics. Mendel showed that hereditary traits (inclinations) are not "fused", as previously thought, but are transmitted from parents to descendants in the form of discrete (isolated, separate) units, which he called factors. These units, presented in pairs in individuals, do not merge together, but remain discrete and are transmitted to descendants in male and female germ cells, one unit from each pair.

In 1909, the hereditary units were named by the Danish scientist W. Johansen genes (Greek genos - “genus”). At the beginning of the XX century. the American embryologist and geneticist T. Morgan established experimentally that genes are located on chromosomes and are arranged linearly there. Since then, the concept of the gene has been central to genetics.

Prominent role in the development of genetics in the first half of the XX century. played by our domestic scientists. A.S. Serebrovsky, exploring the genetics of animals, showed the complex structure of the gene, introduced the term "gene pool" into science. The doctrine of heredity and variability was enriched by the works of N.I. Vavilov, who formulated in 1920 the law of homological series of heredity and variability, which ensured a close connection between genetics and evolutionary doctrine. Yu.A. Filipchenko conducted numerous experiments on the genetic analysis of plants, developed methods for studying variability and heredity. A significant contribution to the development of genetics was also made by G.D. Karpechenko, N.K. Koltsov, S.S. Chetverikov and other researchers.

In the 40s. the biochemical foundations of genetics were laid. Scientists have proven the role of nucleic acid molecules in the transmission of hereditary information, which led to the birth of molecular genetics. Deciphering the structure of the DNA molecule, published in 1953, showed a close connection of this chemical compound with hereditary information in genes.

Achievements in the field of molecular genetics have led to the creation of a new branch of biological science - genetic engineering, which allows, by manipulating individual genes, to obtain in vitro new combinations of genes in the chromosome that did not exist before. Genetic engineering has become widely used in the practice of agriculture and biotechnology.

Genetics is the theoretical basis of selection (lat. selectio - “choice”, “selection”) of plants, animals and microorganisms, that is, the creation of organisms with the properties that a person needs. Based on genetic patterns, breeders create improved plant varieties and breeds of domestic animals. Genetic engineering methods produce new strains (pure cultures) of microorganisms (bacteria, fungi) that synthesize substances for the treatment of diseases.

The research of genetic scientists has led to the understanding of the fact that along with infectious diseases, there are many different hereditary diseases. Early diagnosis of these diseases allows timely intervention in the course of the disease and prevent or slow down its development.

Environmental degradation and negative environmental changes have caused many disorders in the genetic sphere of living organisms, increasing the likelihood of hereditary diseases in humans.

The scientific and practical role of genetics is determined by the significance of the subject of its study - heredity and variability, that is, the properties inherent in all living beings.

1. What does the science of genetics study, when and why did it get its name?

2. Why is G. Mendel considered the "father of genetics"?

3. Replace the highlighted words with the term.

The data of science, which studies the heredity and variability of organisms, are now widely used in all areas of biology.

Units that ensure the transfer of hereditary properties are present in all organisms without exception.

4*. Describe the role of knowledge about nucleic acids for the development of genetics.

§ 18 Basic concepts of genetics

Genetics studies two main properties of living organisms - heredity and variability.

Heredity is the ability of organisms to transmit their characteristics and characteristics of development to offspring. Thanks to this ability, all living beings (plants, animals, fungi or bacteria) retain the characteristic features of the species in their descendants. Such continuity of hereditary properties is ensured by the transfer of their genetic information. Genes are the carriers of hereditary information in organisms.

A gene is a unit of hereditary information that manifests itself as a sign of an organism.

In the topic “Protein biosynthesis in a living cell” (§ 10), it was noted that a gene serves as the basis for building protein molecules, but in genetics, a gene acts as a carrier of a trait in an organism. This “duality” of the gene becomes understandable if we recall that the most important function of a protein in a cell is enzymatic, that is, the control of chemical reactions, as a result of which all the signs of an organism are formed. This "dual" role of the gene can be expressed by the scheme: gene -" protein -\u003e enzyme -\u003e chemical reaction -\u003e sign of the organism.

A gene is a section of a DNA molecule that determines the possibility of developing a particular trait. However, the very development of this feature is largely dependent on external conditions.

The totality of all genes (alleles) of an individual is called the genotype. The genotype acts as a single interacting system of all genetic elements that control the manifestation of all the signs of the organism (development, structure, vital activity).

The genotype determines the limits (range) of the norm of the reaction of the organism, i.e., its genetic capabilities, and the phenotype implements these capabilities in signs.

Each organism lives and develops in certain environmental conditions, experiencing the action of external factors. These factors (temperature, light, the presence of other organisms, etc.) may manifest themselves in the phenotype, i.e., the size or physiological properties of the organism may change. Therefore, the manifestation of signs even in closely related organisms can be different. These differences between individuals within a species are called variability.

Variability is a property of living organisms to exist in various forms, providing them with the ability to survive in changing environmental conditions.

Variation is a property of organisms, opposite to heredity. But both heredity and variability are inextricably linked. They ensure the continuity of hereditary properties and the ability to adapt to changing new environmental conditions, causing the progressive development of life.

Heredity and variability are inherent in all organisms. Genetics, studying the patterns of heredity and variability, reveals methods for managing these processes.

1. What is an allele? What genes are called allelic?

2. Compare the role of heredity and variability in the life of organisms.

3*. Eliminate words in sentences that distort the correctness of the statements.

A gene as a hereditary factor and a discrete unit of genetic information is localized in the chromosomes of organelles.

A genotype is a single system of all chromosomes and genetic elements of a given cell or organism.

The limits of the reaction norm are determined by the genotype and phenotype.

Anaphase. Microtubules contract, centromeres separate and move away from each other. The chromosomes separate and the chromatids move to opposite poles of the spindle.

Simultaneously with telophase, the division of the cytoplasm begins. First, a constriction (partition) is formed between the daughter cells. After some time, the contents of the cell are divided. This is how new daughter cells appear with cytoplasm around new identical nuclei. After that, the preparation for the division of the now new cell begins again, and the whole cycle is repeated continuously, if there are favorable conditions. The process of mitosis takes about 1-2 hours. Its duration varies in different types of cells and tissues. It also depends on environmental conditions.

The division of the nucleus and, consequently, the cell goes on continuously as long as the cell has the means to ensure its vital activity.

Cell cycle. The existence of a cell from the moment it appears as a result of division to division into daughter cells is called cell life cycle or cell cycle. There are two stages (or stages) in the cell life cycle.

First step of the cell cycle- preparation of the cell for division. It is called interphase (from Latin inter- “between” and Greek phasis- “appearance”). Interphase in the cell cycle takes the longest (up to 90%) time interval. During this period, the nucleus and nucleolus are clearly visible in the cell. There is an active growth of a young cell, biosynthesis of proteins, their accumulation, preparation of DNA molecules for doubling and doubling (replication) of all chromosome material is carried out. Chromosomes are not visible, but the process of their doubling is actively going on. A doubled chromosome consists of two halves containing one double-stranded DNA molecule. Characteristic features of interphase cells are despiralization (unwinding) of chromosomes and their uniform distribution in the form of a loose mass throughout the nucleus. By the end of the interphase, the chromosomes spiralize (twist) and become visible, but still represent thin elongated threads (Fig. 22).

At the second stage of the cell cycle Mitosis occurs and the cell divides into two daughter cells.

After separation, each of the two daughter cells again enters the interphase period. From this moment on, both eukaryotic cells that have arisen begin a new (now their own) cell cycle.

As you can see, cell division in eukaryotes and prokaryotes occurs in different ways. But both simple division in prokaryotes and division by mitosis in

eukaryotes are methods of asexual reproduction: daughter cells receive the hereditary information that the parent cell had. Daughter cells are genetically identical to the parent. Any changes in genetic

apparatus does not occur here. Therefore, all cells that appear in the process of cell division and the tissues formed from them have genetic homogeneity.

1. Explain the differences in the processes of cell division in prokaryotes and eukaryotes. 2*. Why are the offspring identical to the parent in asexual reproduction?

3. Describe the process of mitosis and the features of each of its stages.

4. Replace the underlined words with terms.

First phase of mitosis begins when chromosomes become visible

At the end of the third phase of mitosis Chromosomes are at opposite poles of the cell.

Cell structures containing genetic information become visible only during mitosis.

Laboratory work No. 2 (see Appendix, p. 230).

§ 15 Formation of sex cells. Meiosis

sex cells (gametes) develop in the genital (generative) organs and play a crucial role: they ensure the transfer of hereditary information from parents to offspring. During sexual reproduction, as a result of fertilization, two germ cells (male and female) merge and form one cell - a zygote, the subsequent division of which leads to the development of a daughter organism.

only germ cells are haploid. In all other cells of the body of these organisms, the nucleus contains a diploid (2p) - a double set of chromosomes.

With the help of meiosis, germ cells are formed with a smaller set of chromosomes and with qualitatively different genetic properties than those of the parent cells.

Meiosis, or reduction division, is a combination of two peculiar stages of cell division, following each other without interruption. They are called meiosis I (first division) imeiosis II (second division). Each stage has several phases. The names of the phases are the same as the phases of mitosis. Interphases are observed before divisions. But doubling of DNA in mitosis occurs only before the first division. The course of meiosis

shown in figure 23.

AT first interphase(preceding the first division of meiosis) there is an increase in cell size, doubling of organelles and doubling of DNA in chromosomes.

First division (meiosis I) begins with prophase /, during which duplicated chromosomes (having two chromatids each) are clearly visible in a light microscope. In this phase, identical (homologous) chromosomes, but originating from nuclei

paternal and maternal gametes, approach each other and "stick together" along the entire length in pairs. The centromeres (constrictions) of homologous chromosomes are located side by side and behave as a single unit, holding the four chromatids together. Such interconnected homologous doubled chromosomes are called a pair or a bivalent (from Latin bi - “double” and valens - “strong”).

The homologous chromosomes that make up the bivalent are closely connected to each other at some points. In this case, an exchange of sections of DNA strands can occur, as a result of which new combinations of genes in the chromosomes are formed. This process is called crossing door (English cmssingover - "cross"). Crossing over can lead to recombination of large or small sections of homologous chromosomes with several genes or parts of one gene in DNA molecules (Fig. 24).

Due to crossing over, chromosomes with other hereditary properties in comparison with the chromosomes of parental gametes turn out to be in germ cells.

The phenomenon of crossing over is of fundamental biological importance, as it increases the genetic diversity in the offspring.

The complexity of the processes occurring in prophase I (in chromosomes, nucleus) determines the longest duration of this stage of meiosis.

In metaphase I, bivalents are located in the equatorial part of the cell. Then,

in anaphase I, homologous chromosomes diverge to opposite poles of the cell. Telophase / completes the first division of meiosis, as a result of which two daughter cells are formed, although each chromosome in them still remains doubled (i.e., consists of two sister chromatids).

Telophase I is followed by second interphase. She takes very

a short time, since DNA synthesis does not occur in it.

The second division (meiosis II) begins with prophase II.

Two daughter cells that have arisen in telophase I begin division similar to mitosis: the nucleoli and nuclear membranes are destroyed, spindle filaments appear, with one end attached to the centromere. In metaphase, the chromosomes line up along the equator of the spindle. In vanaphase II, the centromeres divide, and the chromatids of the chromosomes in both daughter cells diverge towards their poles.

AT As a result of meiosis, four cells with a haploid set of chromosomes appear from one cell.

The process of formation of male germ cells (spermatozoa) is called spermatogenesis(from the Greek spermatos - "seed" and genesis - "emergence", "origin"). The process of development of female germ cells (ova) is called ovogenesis or oogenesis (from the Greek oop - “egg” and genesis - “emergence”, “origin”),

1. Why are the properties of the daughter organisms that developed from the zygote not identical to those of the parent?

2*. What is the biological meaning of meiosis?

3. Replace the highlighted words with the term.

Cell division, as a result of which there are half as many chromosomes in the nucleus, leads to the formation of germ cells.

§ 16 Individual development of organisms - ontogenesis

The body undergoes significant transformations during the period of its life: it grows and develops.

The set of transformations that occur in the body from its inception to natural death is called individual development iontogenesis

(from the Greek ontos- “existing” and genesis- “emergence”, “origin”). In unicellular organisms, life fits into one cell cycle and all transformations occur between two cell divisions. In multicellular organisms, this process is much more complicated.

Unicellular organisms, like all cells, arise by cell division. In a newly formed cell, intracellular structures are not always formed that provide its specific functions and life processes. It takes a certain time for all organelles to form and all the necessary enzymes to be synthesized. This early period of existence of a cell (and a single-celled organism) in the cell cycle is called maturation. It is followed by a period of the mature life of the cell, ending with its division.

In the individual development of a multicellular organism, several stages are distinguished, which are often called age periods. There are four age periods: embryonic (embryonic), youth, maturity old age.

In animals, only two periods are often distinguished: embryonic and postembryonic. The embryonic period is the development of the embryo (embryo) before its birth. Postembryonic called the period of development of the organism from its birth or exit from the egg or embryonic membranes to death.

Embryonic period of ontogeny(embryonic development), occurring in utero in the mother's body and ending in birth, is found in most mammals, including humans. In oviparous and spawning organisms, embryonic development occurs outside the mother's body and ends with the release of egg membranes (in fish, amphibians, reptiles, birds, as well as in many invertebrate animals - echinoderms, mollusks, worms

and etc.).

At In the vast majority of animal organisms, the process of embryonic development occurs in a similar way. This confirms the commonality of their origin.

At human in the course of embryonic development, the first to separate the head and spinal

brain. This happens within the third week after conception. At this stage, the length of the human embryo is only 2 mm.

After birth or exit from the egg, postembryonic development organism. For some organisms, this period of life takes several days, for others - several tens and hundreds of years, depending on the species.

Postembryonic development consists of three age periods: youth, maturity old age. Each of these periods is characterized by certain transformations in the structure and life processes of the organism, due to its heredity and the influence of external conditions. In the process of postembryonic development, the organism undergoes quantitative and qualitative changes.

Ontogeny is the development of an individual (individual) due to heredity and the influence of environmental conditions.

The existence of any organism is a complex and continuous process of embryonic and postembryonic development in certain habitat conditions and over the periods characteristic of each species.

1. Describe the period of embryonic development of an organism.

2. Replace the terms with the following definitions: an organism in the early stages of development; individual development of a multicellular organism.

3*. Explain why the influence of dangerous external influences (radiation, smoking) is more destructive at the embryonic stage of ontogenesis than at the postembryonic stage.

The individual development of all organisms is carried out in accordance with the hereditary properties inherent in the species, and depending on the environmental conditions.

Test yourself

1. Explain the biological role of female and male sex gametes.

2. Explain the main differences between mitosis and meiosis.

3. What is the dependence of the individual development of the organism on environmental conditions in the embryonic and postembryonic periods?

4. What stages are observed in the cell cycle of unicellular organisms? Explain the importance of interphase in the life of a cell.

1. Describe the concepts of "growth of the organism" and "development of the organism".

Issues for discussion

1. Describe the biological role of different types of reproduction if they are observed in organisms of the same species. Give examples.

2. Expand the mechanism for ensuring the continuity of life.

Basic concepts

Asexual reproduction. Sexual reproduction. Gamete. Zygote. Chromosome. Mitosis. Meiosis. Crossing over. Cell cycle. diploid cell. haploid cell. Ontogenesis.

Chapter 4 Fundamentals of the doctrine of heredity and variability

After studying the chapter, you will be able to:

explain the basic concepts of genetics;

describe the mechanism of sex determination and types of trait inheritance;

characterize the role of heredity and variability of organisms in wildlife.

§ 17 From the history of the development of genetics

Ancient Chinese manuscripts testify, for example, that 6000 years ago

different varieties of rice through crossbreeding and selection. Archaeological finds confirm that the Egyptians cultivated productive varieties of wheat. Among the Babylonian written monuments in Mesopotamia, a stone tablet was found dating back to the 6th millennium BC. e., which recorded data on the inheritance of the shape of the head and mane in five generations of horses (Fig. 25).

In 1909, the hereditary units were named by the Danish scientist V. Johansen genes (Greek genos - “genus”). At the beginning of the XX century. the American embryologist and geneticist T. Morgan established experimentally that genes are located on chromosomes and are arranged linearly there. Since then, the concept of the gene has been central to genetics.

variability and heredity. A significant contribution to the development of genetics was also made by G.D.

Karpechenko, N.K. Koltsov, S.S. Chetverikov and other researchers.

Genetics is the theoretical basis of selection (Latin selectio - "choice", "selection") of plants, animals and microorganisms, that is, the creation of organisms with the properties that a person needs. Based on genetic patterns, breeders create improved plant varieties and breeds of domestic animals. Genetic engineering methods produce new strains (pure cultures) of microorganisms (bacteria, fungi) that synthesize substances for the treatment of diseases.

The research of genetic scientists has led to the understanding of the fact that along with infectious diseases, there are many different hereditary

The formation of germ cells. Meiosis

Remember

the importance of sexual reproduction of organisms in nature;

the role of germ cells in sexual reproduction.

Meiosis is a special type of cell division. The nucleus of somatic (body) eukaryotic cells contains two sets of identical chromosomes - one from both parents. Such cells are called diploid (Greek diploos - "double" and eidos - "kind").

Two parent individuals take part in sexual reproduction. An important role in this process is played by gametes - male and female.

sex cells. Through the hereditary information contained in them, they transfer the properties of a certain type of organisms from parents to descendants. Thus, the continuity of generations and the continuity of the existence of species is carried out.

The number of chromosomes in each species during sexual reproduction remains constant. This is due to the fact that germ cells are formed by a special division. Thanks to him, not two, but only one set of chromosomes gets into the nucleus of each gamete. Reducing the number of chromosomes in the nucleus is called reduction (from Latin reducere - “bring back”, “return”). Cells with a single set of chromosomes are called haploid (Greek haploos - "simple", "single" and eidos - "view"). The haploid set is usually referred to as n, and the diploid 2 n.

The process of cell division, as a result of which half the number of chromosomes in the nucleus of daughter cells, is called meiosis (Greek meiosis - “reduction”). As a result of fertilization (fusion of male and female gametes), a zygote is formed - the first cell of the future organism. The meeting of parental gametes during fertilization is random. In the zygote, the hereditary information received from the parents is combined and the diploid set of chromosomes is restored.

For example, in humans, each sex cell (both sperm and egg) normally contains 23 chromosomes. During the formation of a zygote, the nucleus of germ cells merge and their chromosomes unite in pairs. Thus, there are 46 chromosomes in the zygote. Chromosomes that form pairs with each other are called homologous (Greek homoios - “similar”, “same”).

Meiosis, or reduction division, is a combination of two peculiar stages of cell division, following each other without interruption. They are called meiosis I (first division) and meiosis II (second division). Each stage has several phases. The names of the phases are the same as those of the phases of mitosis. Interphases are observed before divisions. But the duplication of DNA in meiosis occurs only before the first division.

In the interphase preceding the first division of meiosis, there is an increase in cell size, doubling of organelles and doubling of DNA in chromosomes.

First division of meiosis. Meiosis I begins with prophase I, during which duplicated chromosomes (consisting of two chromatids) are clearly visible under a light microscope. In this phase, identical (homologous), but originating from the nuclei of the paternal and maternal gametes, the chromosomes approach each other. The centromeres (constrictions) of homologous chromosomes are located side by side and behave as a single unit, holding the four chromatids together. Such interconnected homologous doubled chromosomes called pair or bivalent

The homologous chromosomes that make up the bivalent are closely connected to each other at some points. In this case, an exchange of sections of DNA strands can occur, as a result of which new combinations of genes in the chromosomes are formed. This process is called crossing over (eng. crxtssingover - "cross". Crossing over can lead to the recombination of small or large sections of homologous chromosomes with several genes.

Due to the crossover, chromosomes with other hereditary properties in comparison with the chromosomes of the parental gametes turn out to be in the germ cells.

The phenomenon of crossover is of fundamental biological importance, as it increases the genetic diversity of offspring.

In metaphase I, bivalents are located in the equatorial part of the cell. Then, in anaphase I, homologous chromosomes separate to opposite poles of the cell. Telophase I completes the first division of meiosis, which results in the formation of two daughter cells. Each chromosome in them still remains doubled (that is, it consists of two sister chromatids).

After. telophase I begins the second ipterphase. It takes a very short time, since DNA synthesis does not occur in it.

Second division of meiosis. Meiosis II begins with prophase II. Two daughter cells that have arisen in telophase I begin division similar to mitosis: the nucleoli and nuclear membranes are destroyed, spindle filaments appear, attaching to the centromeres at one end. In metaphase II, the chromosomes line up along the equator of the spindle. In anaphase II, the centromeres divide and the chromatids move toward the poles of the cell.

In telophase II, a nuclear membrane forms around the nucleus, which now contains a single (haploid) set of chromosomes, and the cytoplasm separates. The reduction process of the formation of germ cells ends with the creation of four haploid cells - gametes.

As a result of meiosis, four cells with a haploid set of chromosomes appear from one cell.

The process of formation of male germ cells (spermatozoa) is called spermatogenesis (Greek spermatos - "seed" and genesis - "emergence", "origin"), female germ cells (eggs) - oogenesis.

Meiosis occurs in the life cycles of very many organisms and is of great importance in the living world. In the process of meiosis (unlike mitosis), daughter cells are formed that contain half as many chromosomes as the parent cells. However, due to the interaction of chromosomes originating from the father and mother, the offspring acquires qualitatively new, unique features due to the recombination of genes in the chromosomes. The emergence of many new combinations of genes increases the ability of the species to develop adaptations to changing environmental conditions, which plays an important role in evolution. In the figure, carefully consider how the chromosomes are arranged and how they diverge in the phases of meiosis. Comment on the change in the properties of homologous chromosomes that occurred as a result of their crossing.

year 2013

Instructions for completing the task

You are offered tasks that meet the minimum knowledge requirements of graduates of the basic school in the subject "Fundamentals of Life Safety".

Assignments are presented in the form of unfinished statements, which, when completed, can be either true or false.

Approvals are presented in:

In a closed form, that is, with proposed completion options, when performing these tasks, you must choose the correct completion from the 4 proposed options. Among them are both correct and incorrect completions, as well as partially corresponding to the meaning of the statement. Only one is correct - the one that most fully corresponds to the meaning of the statement. The selected options are marked by crossing out the corresponding box in the answer sheet: “a”, “b”, “c” or “d”;

Open form, that is, without the proposed completion options. When completing this task, you must independently choose a word that, completing the statement, forms a true statement. The selected word fits into the appropriate column of the answer sheet;

A form that involves establishing the order of the directions, systems, characteristics, indicators, sizes known to you. The selected option is marked by crossing out the corresponding box in the answer sheet: “a”, “b”, c” or “d”.

Entries must be legible.

Read the questions and possible answers carefully. Try not to guess, but logically justify your choice. Skip unfamiliar tasks instead of completing them by guesswork. This will save time for other tasks. Later, you can return to the missed task. The time for completing tasks is 90 minutes.

1. You are in a forest where a fire broke out. Determine the sequence of actions.

1) quickly leave the forest in the direction of the wind

2) determine the direction of the spread of fire

3) choose an exit route from the forest to a safe place

4) determine the direction of the wind

a) 4, 2, 3, 1

b) 1, 2, 3, 4

in) 3, 2, 4, 1

G) 2, 1, 4, 3

2. Complete the statement by writing the appropriate word on the answer sheet.

... - an organ of the human body in which blood from venous turns into arterial.

3. Determine what to do after reporting an accident at a chemical plant near your home. You do not have individual means protection, shelter, as well as the possibility of exit from the accident zone:

1) turn on the radio, TV, listen to information

2) close the entrance doors with a thick cloth

3) tightly close all windows and doors

4) to seal the dwelling

a) 1, 2, 3, 4

b) 2, 1, 3, 4

in) 4, 2, 1, 3

G) 3, 2, 1, 4

4. Nuclear weapons are:

a) precision offensive weapons based on the use of ionizing radiation when a nuclear charge explodes in the air, on the ground (on water) or underground (under water)

b) weapons of mass destruction of explosive action, based on the use of light radiation as a result of a large flow of radiant energy arising from the explosion, including ultraviolet, visible and infrared rays

in) explosive weapons of mass destruction based on the use of intranuclear energy

G) spontaneous transformation of unstable atomic nuclei into nuclei of other elements, accompanied by the emission of nuclear radiation

5. Once in the zone of chemical contamination, you smelled bitter almonds. What is this poisonous substance?

a) mustard gas

b) sarin

in) hydrocyanic acid

G) phosgene

6. In case of simultaneous contamination with radioactive, toxic substances and bacterial (biological) agents, the following shall be neutralized first of all:

a) toxic substances, and then radioactive substances and bacterial (biological) agents

b) radioactive substances and bacterial (biological) agents, and then toxic substances

in) bacterial agents, and then radioactive and poisonous substances

G) radioactive substances, and then bacterial and poisonous

7. Complete the statement by writing the appropriate word on the answer sheet.

The state of deep depression of the central nervous system, in which consciousness and reaction to external stimuli are lost, there is a disorder in the regulation of vital body functions, is called ...

8. Determine the correct sequence of first aid for closed fractures:

a) stop bleeding, apply a sterile bandage, give an anesthetic, immobilize the limb, take the victim to a medical facility

b) put a tight bandage on the fracture site, give painkillers, take the victim to a medical facility

in) give an anesthetic, immobilize, deliver the victim to a medical facility

G) carry out immobilization, apply cold to the fracture site, deliver the victim to a medical facility

9. Complete the statement by writing the appropriate definition on the answer sheet.

Restoration or temporary replacement of impaired or lost vital functions of the body with the help of certain external influences is called ...

10. Complete the statement by writing the appropriate word on the answer sheet.

A formation in which the military personnel are located at the back of each other's head, and the units (vehicles) - one after the other at distances set by the commander, is called ...

11. The battle of the Russian troops led by Alexander Nevsky with the knights of the Livonian Order on the ice of Lake Peipus took place in ... year.

a) 1242 b) 1380 in) 1223 G) 1283

12. Poisonous substances (OS) that cause acute burning of the respiratory organs, eyesight, lacrimation, cough, making breathing difficult, belong to the OV:

a) general poisonous

b) psychochemical

in) annoying

G) nerve agent

13. Complete the statement by writing the appropriate word on the answer sheet.

Mechanical mixtures of iron oxides with aluminum, ignited by a special ignition device, burning in the absence of oxygen and creating temperatures up to 3000 ° C, are called. . .

14. The physical and mental state of the human body, which is in conditions of social and environmental well-being, in which it has high performance and feels satisfaction from its life activity, is called:

a) happiness

b) well-being

in) satisfaction

G) health

15. Complete the statement by writing the appropriate word on the answer sheet.

a) trash, paper

b) gasoline, kerosene

in) wooden buildings

b) chlorine

in) phosgene

G) ammonia

25. An ammonia leak occurred during an accident at a chemically hazardous facility. You live on the fourth floor of a nine-story building. What will you do if your house is in the zone of infection?

a) stay in your apartment

b) hide in the basement of a building

in) go up to the top floor

G) ventilate the room and stay in your apartment

26. During an accident at a chemically hazardous facility, chlorine leaked. You may be in the infection zone, you live on the first floor of a nine-story building. How will you do it?

a) hide in the basement of a building

b) go up to the top floor

in) stay in your apartment

G) leave your apartment and go down to the first floor

27. An explosive mixture consisting of petroleum products and additives of powdered magnesium (aluminum), liquid asphalt and heavy oils is:

a) napalm

b) thermite mixtures

in) incendiary mixture "Electron"

G) pyrogels

28. Unicellular non-nuclear organisms that are heterotrophs that cause infectious diseases are called pathogens:

a) mushrooms

b) viruses

in) protozoa

G) bacteria

29. Complete the statement by writing the appropriate definition on the answer sheet.

The damaging factor of nuclear weapons, which causes significant destruction of material objects and mechanically destroys the enemy's manpower, is called ....

30. Find among the names of groups of organisms listed below and individual organisms one that can cause infectious diseases:

a) insects

b) rodents

in) amphibians

G) unicellular fungi

31. What GO signal means the howling of a siren, intermittent beeps of enterprises and vehicles?

a) Air Raid

b) radiation hazard

in) Attention everyone

G) chemical hazard

32. Find among the listed names of diseases one that is not infectious:

a) cholera

b) tetanus

in) hepatitis A

G) pediculosis

33. From the following, select one reason for forced autonomous existence in natural conditions:

a) lack of communication

b) untimely registration of the tourist group before going on the route

in) large forest fire

G) compass loss

34. Indicate the number of growths of the combined arms gas mask.

a) 3 b) 4 in) 5 G) 6

35. The area of low pressure in the atmosphere is:

a) tornado b) cyclone in) storm G) anticyclone

36. What is the difference between bacteriological weapons and chemical weapons mass destruction?

37. Define what an emergency is.

38. Describe the procedure for putting on a gas mask.

39. Name the dimensions of the OZK.

40. Name the premises that are in the shelter.