Body cells that have a diploid set of chromosomes. Homologous chromosomes, diploid set of chromosomes
Children inherit certain genes from their parents. As you know, the younger generation "takes" from the older one the shape of the face, features of the head, hands, hair color, etc.). For the transfer of signs to children from parents in the body, such a substance is responsible. This unique substance contains biological information about variability. It is written in code. The chromosome stores it.
The human cell contains twenty-three pairs of such structural and functional units as chromosomes. Each such "duet" contains two absolutely identical structural and functional units. The difference is that these couples are different from each other. Chromosomes numbered forty-five and forty-six are the sex chromosomes. Moreover, this duet is the same only for girls, for men they are different. All structural and functional units, with the exception of sex, are called "autosomes". It should be noted that chromosomes are mostly composed of elements such as proteins. They are different in appearance: some of them are thinner, others are somewhat shorter than others, but each of them has a twin. The chromosome set (or, as it is also called, the karyotype) of a person is a genetic structure that is responsible for the transmission of heredity. It is better to consider such structural and functional units under a microscope at the time (metaphase stage). During this period, chromosomes are formed from a substance such as chromatin, and are already beginning to acquire a certain amount, i.e. ploidy.
As noted above, a human cell has twenty-three pairs of important structural and functional elements. Living organisms have their own individual ploidy.
Haploid and diploid set of chromosomes. The concept of ploidy is defined as the number of chromosome sets in cells (mainly) in nuclei. In living organisms, chromosomes can be unpaired or paired. In human cells, a diploid set of chromosomes is formed, that is, a double set. Such a set of structural and functional elements is characteristic of all somatic cells. It is worth noting that each person has a diploid set of chromosomes consisting of 44 autosomes and 2 sex chromosomes. The haploid set of chromosomes is a single set of unpaired structural and functional elements. This set contains twenty-two autosomes and only one sex chromosome. A haploid set and a diploid set of chromosomes can be present at the same time. This occurs mainly during the sexual process. At this point, the haploid and diploid phases alternate. With division, the full set forms a single set. After that, two single ones are connected and form a complete set of structural and functional elements, etc.
The diploid set of chromosomes is a set of chromosomes that is inherent in all somatic cells. In it, all chromosomes that are characteristic of a given biological species are presented in pairs. In each person, the diploid set of chromosomes is capable of containing forty-four autosomes and two sexual structural and functional elements. The diploid set of chromosomes is characteristic of the zygote and all somatic cells, except for ansuploid, haploid and polyploid cells.
It also happens that there is a violation of the set of structural and functional units. Failures can affect education (for example, Down's Syndrome - the formation of triosomy, i.e. violations in the twenty-first pair and the appearance (third)). The study of chromosomes is very important, since these elements have a very serious effect on the human body.
diploid set
"... A diploid set is a set of chromosomes in the somatic cells of an organism that contains two homologous sets of chromosomes, of which one is transmitted from one parent, and the second from the other ..."
(approved by the Chairman of the Health Committee of Moscow on January 17, 2000)
Official terminology. Akademik.ru. 2012 .
See what "Diploid set" is in other dictionaries:
diploid set- A complete set of genetic material contained in paired chromosomes Biotechnology topics EN diploid …
DIPLOID SET- The normal number of chromosomes in somatic cells of certain species. In humans, the diploid set is 46. The diploid set is a double haploid set ... Explanatory Dictionary of Psychology
diploid set- (Greek diploos double) the normal number of chromosomes in somatic cells (in humans 46) ... Encyclopedic Dictionary of Psychology and Pedagogy
Diploid set of chromosomes- * diploid chromosome number …
diploid set of chromosomes- ANIMAL EMBRYOLOGY DIPLOID SET OF CHROMOSOMES, DOUBLE SET OF CHROMOSOMES (2p) - a set of chromosomes containing two copies of each of the homologous chromosomes ... General Embryology: Terminological Dictionary
diploid set of chromosomes- diploidinis chromosomų rinkinys statusas T sritis augalininkystė apibrėžtis Du haploidiniai chromosomų rinkiniai, turintys tik vieno arba abiejų tėvų chromosomas. atitikmenys: engl. diploid chromosome set rus. diploid set of chromosomes... Žemės ūkio augalų selekcijos ir sėklininkystės terminų žodynas
diploid set of chromosomes- (syn.: double set of chromosomes, zygotic set of chromosomes, complete set of chromosomes, somatic set of chromosomes) a set of chromosomes inherent in somatic cells, in which all chromosomes characteristic of a given biological species are represented ... Big Medical Dictionary
DIPLOID SET OF CHROMOSOMES- double the number of chromosomes in the zygote and somatic cells of an adult organism ... Glossary of botanical terms
diploid (somatic) parthenogenesis- A form of parthenogenesis in which the egg contains an unreduced (diploid) set of chromosomes. [Arefiev V.A., Lisovenko L.A. English Russian explanatory dictionary of genetic terms 1995 407s.] Topics genetics EN diploid ... ... Technical Translator's Handbook
Diploid parthenogenesis, somatic p- Diploid parthenogenesis, somatic p. or parthenogamy, a form of parthenogenesis in which the egg contains an unreduced (diploid) set of chromosomes ... Genetics. encyclopedic Dictionary
Chromosomes are dense, intensely staining structures that are units of the morphological organization of genetic material and ensure its precise distribution during cell division. The number of chromosomes in the cells of each biological species is constant. Usually in the nuclei of body cells (somatic) chromosomes are presented in pairs, in germ cells they are not paired. Vasilyeva V.I., Volkov I.M., Yarygin V.N., Sinelshchikova V.V. Biology. 2 book. Book. 1. M: Higher School, 2004. - 76-78s.
A single set of chromosomes in germ cells is called haploid (n), a set of chromosomes in somatic cells is called diploid (2n). The chromosomes of different organisms differ in size and shape. A diploid set of chromosomes in cells of a particular type of living organisms, characterized by the number, size and shape of chromosomes, is called a karyotype. In the chromosome set of somatic cells, paired chromosomes are called homologous, chromosomes from different pairs are called non-homologous. Homologous chromosomes are the same in size, shape, composition (one is inherited from the maternal, the other from the paternal organism). The chromosomes in the karyotype are also divided into autosomes, or non-sex chromosomes, which are the same in male and female individuals, and heterochromosomes, or sex chromosomes involved in sex determination and differing in males and females. The human karyotype is represented by 46 chromosomes (23 pairs): 44 autosomes and 2 sex chromosomes (the female has two identical X chromosomes, the male has X and Y chromosomes).
During sexual reproduction, the genomes of two parental germ cells combine to form the genotype of a new organism. All somatic cells of such an organism have a double set of genes received from both parents in the form of certain alleles. Thus, the genotype is the genetic constitution of the organism, which is the totality of all the hereditary inclinations of its cells, contained in their chromosome set - the karyotype.
Karyotypes of organisms of various species are shown in Figure 1.
Rice. one. Karyotypes of organisms of various species: I - skerds, II - Drosophila. III - human
Karyotype - a diploid set of chromosomes, characteristic of the somatic cells of organisms of a given species, which is a species-specific feature and is characterized by a certain number, structure and genetic composition of chromosomes (Fig. 3.67). Below are the numbers of chromosomes of somatic cells of some types of organisms.
If the number of chromosomes in the haploid set of germ cells is denoted by n, then the general karyotype formula will look like 2n, where the value of n is different in different species. Being a species characteristic of organisms, the karyotype may differ in individual individuals by some particular features. For example, representatives of different sexes have basically the same pairs of chromosomes (autosomes), but their karyotypes differ in one pair of chromosomes (heterochromosomes, or sex chromosomes). Sometimes these differences consist in a different number of heterochromosomes in females and males (XX or XO). More often, the differences relate to the structure of the sex chromosomes, denoted by different letters - X and Y (XX or XY). Vasilyeva V.I., Volkov I.M., Yarygin V.N., Sinelshchikova V.V. Biology. 2 book. Book. 1. M: Higher school, 2004. - 112 p.
Each type of chromosome in the karyotype containing a certain complex of genes is represented by two homologues inherited from parents with their germ cells. A double set of genes enclosed in a karyotype - a genotype - is a unique combination of paired alleles of the genome. The genotype contains the development program of a particular individual. - a complete haploid set of genes or chromosomes of a cell or organism.
In biology, the term "ploidy" is used to refer to the number of sets contained in a . Different organisms have different numbers of chromosomes. Two types of cells are also diploid cells, the main difference of which is the number of sets of chromosomes in their nuclei.
Diploid cells are cells with two sets of chromosomes. In diploid organisms, each parent passes on one set of chromosomes, which combine into two sets in the offspring. Most mammals are diploid organisms, meaning that there are two homologous copies of each chromosome in the cells. Humans have 46 chromosomes. most diploid organisms, with the exception of (a) are diploid and contain two sets of chromosomes.
Diploid cells divide with the help of which a completely identical copy of the cell is formed. In humans, somatic cells (or non-sex cells) are all diploid cells. These include the cells that make up organs, muscles, bones, skin, hair, and any other part of the body other than eggs (in women) or sperm (in men).
diploid number
The diploid number of a cell is the number of chromosomes in the nucleus of the cell. This number is usually denoted as 2n, where n is equal to the number of chromosomes. For a person, this equation has the following form 2n=46 . Humans have 2 sets of 23 chromosomes, for a total of 46 chromosomes:
- Non-sex chromosomes: 22 pairs of autosomes.
Sex chromosomes: 1 pair of gonosomes.
The difference between haploid and diploid cells
The main difference between haploid and diploid cells is the number of sets of chromosomes contained in the nucleus. Ploidy is a biological term that characterizes the number of chromosomes in a cell. Therefore, cells with two sets are diploid, and cells with one set are haploid.
In diploid organisms such as humans, haploid cells are only used for reproduction, while the rest of the cells are diploid. Another difference between haploid and diploid cells is how they divide. Haploid cells reproduce with help, while diploid cells go through mitosis.
Chromosomal sets of somatic cells of male and female individuals of each species differ in one pair of chromosomes. This pair is the sex chromosomes, or heterochromosomes. All other pairs of chromosomes, the same in both sexes, have a common name - autosomes.
For example, in the human karyotype, pairs of chromosomes that are the same for women and men are autosomes. One pair - the twenty-third - in men and women determines the sex. Therefore, the chromosomes that make up it are called sex chromosomes. This pair in women is homologous (XX), and in men it is heterologous (XY). That is why sex chromosomes are also called heterosomes (from "hetero" - different).
Chromosome Rules
1. The rule of constancy of the number of chromosomes. The number of chromosomes in a cell is constant in every species. That is, the number of chromosomes and the characteristic features of their structure are a species trait. For example, in humans - 46, chimpanzees - 48, fruit flies - 8 chromosomes (general formula -2a).
2. The rule of chromosome pairing. Chromosomes in a diploid set form pairs. Those chromosomes that belong to the same pair are called homologous. These chromosomes are similar in size, shape, location of centromeres, and the set of genes they contain. In each pair, one chromosome is from the mother, the other is from the father.
3. The rule of individuality. Chromosomes of different pairs differ from each other: in size; form; the location of the constrictions; by striation, revealed by special coloring - DOC (differential staining of chromosomes); according to the set of genes they contain. The set of genes of one pair is no longer repeated in any other pair.
4. The rule of chromosome continuity. Each new generation has the same structure and shape of chromosomes as the previous one, i.e., chromosomes from generation to generation retain a relatively constant shape and structure. This is possible because DNA is capable of reduplication (self-doubling).
Thus, one more definition of a karyotype can be given: a karyotype is a set of chromosomes of a somatic cell, which is characterized by a constant number of chromosomes for the species, their size, shape and location of centromeres in them.
The only way for the formation of new cells is the division of previous cells.
The life or cell cycle is the time from the appearance of a cell to its death or the formation of new cells from it, that is, it is its ontogeny.
The mitotic cycle is the life of a cell from the moment of its appearance to the end of its division with the formation of two new cells. (This is one of the variants of the cell cycle).
There are cells whose life cycle coincides with the mitotic cycle. These are cells that are constantly dividing. For example, cells of the skin epidermis, testicles (renewable cell complexes). There are cells that do not have a mitotic cycle (stable cell complexes). These cells lose their ability to divide (eg erythrocytes, neurons). But it has been shown that such a state can be reversible. For example, if a nucleus is removed from a frog egg and the nucleus of a nerve cell is transplanted there, it begins to divide. Based on this, we can conclude that the cytoplasm of the egg contains substances that activate mitosis.
Described three ways of dividing eukaryotic cells:
Amitosis (direct division);
Mitosis (indirect division);
Meiosis (reduction division).
Amitosis is a division in which the interphase nucleus divides by constriction. There is no condensation of chromosomes. Sometimes, after nuclear fission, the cytoplasm does not divide and binuclear cells are formed. Amitosis has been described in skeletal muscle cells, skin epithelial cells, and also in pathologically altered cells (tumor cells).
Mitosis is a division in which two cells with a diploid set of chromosomes are formed from one cell with a diploid set of chromosomes. This method of division is universal for eukaryotic cells. It underlies the asexual reproduction of organisms. Mitosis is the growth of tissues and the whole organism.
Mitosis is part of the mitotic cycle. The entire mitotic cycle consists of interphase (preparation of the cell for division) + mitosis (the actual division).
Interphase has three periods:
1. Presynthetic - in 1
2. Synthetic - B
3. Postsynthetic - 0 2
Presynthetic period - the cell grows, accumulates ATP, RNA, proteins necessary for the formation of cellular organelles. During this period, the cell acquires features characteristic of this tissue. In this period, the cell has 2n, 2s (n is the haploid set of chromosomes, c is the amount of DNA in one chromatid): i.e., a double set of single chromatid chromosomes.
Synthetic period - DNA reduplication occurs, RNA continues to be synthesized, histone proteins are synthesized. At the end of this period, the cell has 2n,4c: _ i.e., a double set of two-chromatid chromosomes. (The number of chromosomes does not change, but each chromosome already consists of two chromatids).
Postsynthetic period - RNA, proteins necessary for the fission process, ATP, mitochondrial DNA are synthesized. The number of mitochondria, plastids, and centrioles doubles. In this period, the cell has 2p, 4s.,
In interphase, the nucleus is rounded, with clear boundaries. One or more nucleoli are visible in it, Chromosomes - in the form of chromatin, are located in the karyoplasm.
Mitosis is divided into four main phases:
1. prophase;
2. metaphase;
3.anaphase;
4.telophase.
Prophase. The nucleus is markedly enlarged. The nucleoli are removed. Happens. spiralization (condensation, or stacking) of chromosomes: at the beginning of prophase they are thin and long, at the end they are thick and short. Centrioles diverge towards the poles of the cell, the spindle of division begins to form. At the end of prophase, each chromosome is seen to consist of 2 chromatids. Prophase is considered complete when the nuclear envelope breaks up into fragments and the chromosomes enter the cytoplasm. In this period, the cell has 2p, 4s. Each chromosome has two chromatids.
Prometaphase can also be distinguished between prophase and metaphase when chromosomes move towards the equator.
Metaphase. Chromosomes are located at the equator of the cell. A fission spindle thread is attached to each cromatid in the region of the centromere. The chromatids of each chromosome remain connected only in the region of the centromere. In this period, the cell has 2n, 4c (a diploid set of two-chromatid chromosomes).
Anaphase. The chromatids of each chromosome separate from each other at the centromere. The spindle fibers contract and stretch the chromatids (now called daughter chromosomes) to different poles of the cell. In this period, the cell has 4p, 4c (a tetraploid set of single chromatid chromosomes).
Rice. Phases of mitosis
Telophase. At the beginning of the phase, despiralization (unwinding) of chromosomes occurs. A nuclear envelope forms around each cluster of chromosomes. Nucleoli appear. The nuclei take the form of interphase nuclei. The spindle of division gradually disappears. At the end of telophase, cytokinesis occurs, or cytotomy (dividing the cytoplasm of the mother cell). Two daughter cells are formed from one mother cell. They enter the interphase state. In this period, each new cell has 2p, 2c (a double set of single chromatid chromosomes). That is, starting from the anaphase and up to the S-period of the interphase, each chromosome consists of one chromatid.
The biological significance of mitosis
1. Preservation of a constant number of chromosomes in daughter cells (each new cell has the same set of chromosomes as the original - 2p).
2. Uniform distribution of hereditary information between daughter cells.
3. The growth of a new organism during asexual reproduction due to the appearance of new body cells.
4. Regeneration (recovery) of lost cells and organs.
Meiosis is a process consisting of two successive divisions. From one cell with a diploid set of chromosomes (2n, 4c), four haploid cells (n, c) are formed. That is, during meiosis, a reduction (decrease) in the number of chromosomes occurs in the cell.
In each of the divisions of meiosis, the same phases are distinguished as in mitosis: prophase (I and II), metaphase (I and II), anaphase (I and II) and telophase (I and II). But the duration of the individual phases and the processes occurring in them differ significantly from mitosis. The main differences are:
1. Prophase I is the longest. Therefore, it is divided into five stages:
Leptotena: chromosomes begin to spiral;
Zygotene: Homologous chromosomes are conjugated (tightly adjacent to each other along the entire length). Such pairs are called bivalents;
Pachytene: conjugation is complete. Between conjugating chromosomes, an exchange of homologous regions (containing the same genes) can occur - crossing over (or recombination). The sites of exchange are called chiasmata;
Diplotene: repulsive forces arise between homologous chromosomes, first in the centromere region, and then in other areas. It becomes noticeable that these figures consist of four elements. That is, bivalents turn into tetrads. Chromatids in tetrads are linked in the region of telomeres and chiasms;
Diakinesis: chromosomes are maximally spiralized, bivalents are isolated and placed along the periphery of the nucleus. Tetrads shorten, nucleoli disappear.
Meiosis resembles mitosis, but has its own characteristics:
a) In the prophase of the first meiosis, in contrast to mitosis, the conjugation of homologous chromosomes occurs. Between homologous chromosomes there is an exchange of homologous regions, genes (crossing over).
o) In metaphase I, at the equator of the cell, there are homologous chromosomes connected in pairs (one opposite the other) (Fig. 34, metaphase I).
c) During anaphase, it is not chromatids that diverge to the poles (as during mitosis), but two-chromatid homologues (Fig. 34, anaphase I). Therefore, after the first meiotic division, the daughter cells (oocyte II and one polar body during oogenesis and spermatocytes II during spermatogenesis) have a haploid set of chromosomes, but each chromosome consists of two chromatids.
d) Interphase II is very short, because DNA replication is not needed (chromosomes are two-chromatid).
The remaining phases of meiosis II pass quite quickly, not differing from mitotic division. In anaphase, paired sister chromatids separate one by one into daughter cells. Thus, during meiosis, four cells are formed from one original cell (2n, 4c), each with a haploid set of single-chromatid chromosomes (n, s).
The biological significance of meiosis
1. During meiosis, a haploid set of chromosomes is formed in new cells. And during fertilization (fusion of gametes), the diploid set of chromosomes is restored. Thus, in all organisms, the constancy of the number of chromosomes from generation to generation is preserved.
2. During time of two divisions of meiosis, recombination occurs
genetic material due to
a) crossing over;
b) independent divergence of paternal and maternal chromosomes. Combinative variability arises - this provides a variety of material for evolution.
3FEATURES OF THE STRUCTURE OF SEX CELLS (GAMETS)
The eggs are immobile, usually spherical in shape. They contain all the cellular organelles characteristic of somatic cells. But the eggs contain substances (for example, the yolk) necessary for the development of the embryo. Depending on the amount of yolk, the eggs are divided into different types. For example, an isolecithal egg: there is little yolk in it and it is evenly distributed throughout the cytoplasm (the egg of a lancelet, a person). Reptiles and birds have a lot of yolk (telolecithal egg) and it is located at one of the poles of the cell. This pole is called vegetative (nourishing). The opposite pole, where there is little yolk, carries the cell nucleus and is called animal. The type of crushing of the zygote depends on the amount and distribution of the yolk.
The largest egg is in sharks (50 - 70 mm in diameter), in a chicken - more than 30 mm (without protein shells), in a cow - 100 microns, in humans - 130-200 microns.
The eggs are covered with membranes that perform protective and other functions (for example, in placental mammals - for the embryo to grow into the wall of the uterus).
Spermatozoa are small cells (in humans, they have a length of 50-70 microns) and consist of a head, neck and tail. The head contains the nucleus and a small amount of cytoplasm. The acrosome is located at the anterior end of the head. This is a modified Golgi complex. It contains enzymes that break down egg shells during fertilization. The neck contains mitochondria and centrioles. One centriole is proximal (near), it, together with the head, penetrates the egg. The other is distal (far), a tail is attached to it. The mitochondria of the neck provide it with energy. The tail contains microtubules.
Features of germ cells:
They have a haploid set of chromosomes.
In germ cells, compared with somatic cells, less intensive metabolism is noted. The egg cells accumulate substances necessary for the development of the embryo.
Spermatozoa never divide, and the egg, after the introduction of the sperm into it, separates the secondary polocyte (i.e., only now the second division of meiosis is completed in it).