Gene mutations: examples, causes, types, mechanisms. How genes mutate

Waiting for the birth of a child is the most wonderful time for parents, but also the most terrifying. Many are worried that the baby may be born with some kind of handicap, physical or mental disabilities.

Science does not stand still, it is possible to check the baby for developmental abnormalities at a short time in pregnancy. Almost all of these tests can show whether everything is fine with the child.

Why does it happen that completely different children can be born to the same parents - healthy child and a child with disabilities? It is determined by genes. In the birth of an underdeveloped baby or a child with physical disabilities, gene mutations associated with a change in the DNA structure affect. Let's talk about this in more detail. Consider how this happens, what gene mutations are, and their causes.

What are mutations?

Mutations are physiological and biological changes in cells in the structure of DNA. The reason may be radiation (during pregnancy, you can not take x-rays, for the presence of injuries and fractures), ultra-violet rays(long exposure to the sun during pregnancy or being in a room with UV lamps on). Also, such mutations can be inherited from ancestors. All of them are divided into types.

Gene mutations with a change in the structure of chromosomes or their number

These are mutations in which the structure and number of chromosomes are changed. Chromosomal regions can fall out or double, move to a non-homologous zone, turn one hundred and eighty degrees from the norm.

The reasons for the appearance of such a mutation is a violation in crossover.

Gene mutations associated with a change in the structure of chromosomes or their number, are the cause serious disorders and illness in the child. Such diseases are incurable.

Types of chromosomal mutations

In total, two types of basic chromosomal mutations are distinguished: numerical and structural. Aneuploidies are types according to the number of chromosomes, that is, when gene mutations are associated with a change in the number of chromosomes. This is the emergence of an additional or several of the latter, the loss of any of them.

Gene mutations are associated with a change in structure when chromosomes break and then reunite, disrupting the normal configuration.

Types of numerical chromosomes

According to the number of chromosomes, mutations are divided into aneuploidy, that is, species. Consider the main ones, find out the difference.

• trisomy

Trisomy is the occurrence of an extra chromosome in the karyotype. The most common occurrence is the appearance of the twenty-first chromosome. It becomes the cause of Down syndrome, or, as this disease is also called, trisomy of the twenty-first chromosome.

Patau's syndrome is detected on the thirteenth, and on the eighteenth chromosome they are diagnosed. These are all autosomal trisomies. Other trisomies are not viable, they die in the womb and are lost in spontaneous abortions. Those individuals who have additional sex chromosomes (X, Y) are viable. Clinical manifestation these mutations are very few.

Gene mutations associated with a change in number occur according to certain reasons. Trisomy most often occurs during divergence in anaphase (meiosis 1). The result of this discrepancy is that both chromosomes fall into only one of the two daughter cells, the second remains empty.

Less commonly, nondisjunction of chromosomes may occur. This phenomenon is called a violation in the divergence of sister chromatids. It occurs in meiosis 2. This is exactly the case when two absolutely identical chromosomes lodge in one gamete, causing a trisomic zygote. Nondisjunction occurs in early stages the process of crushing an egg that has been fertilized. Thus, a clone of mutant cells arises, which can cover a larger or smaller part of the tissues. Sometimes it manifests itself clinically.

Many associate the twenty-first chromosome with the age of a pregnant woman, but this factor is up to today does not have unequivocal confirmation. The reasons why chromosomes do not separate remain unknown.

• monosomy

Monosomy is the absence of any of the autosomes. If this happens, then in most cases the fetus cannot be borne, there are premature birth on the early dates. The exception is monosomy due to the twenty-first chromosome. The reason why monosomy occurs can be both the nondisjunction of chromosomes and the loss of a chromosome during its journey in anaphase to the cell.

For sex chromosomes, monosomy leads to the formation of a fetus with an XO karyotype. The clinical manifestation of such a karyotype is Turner's syndrome. In eighty percent of cases out of a hundred, the appearance of monosomy on the X chromosome is due to a violation of meiosis of the father of the child. This is due to the nondisjunction of the X and Y chromosomes. Basically, a fetus with an XO karyotype dies in the womb.

According to the sex chromosomes, trisomy is divided into three types: 47 XXY, 47 XXX, 47 XYY. is trisomy 47XXY. With such a karyotype, the chances of carrying a child are divided fifty to fifty. The cause of this syndrome may be the nondisjunction of the X chromosomes or the nondisjunction of X and Y of spermatogenesis. The second and third karyotypes can occur in only one out of a thousand pregnant women, they practically do not manifest themselves and in most cases are discovered by specialists quite by accident.

• polyploidy

These are gene mutations associated with a change haploid set chromosomes. These sets can be tripled or quadrupled. Triploidy is most often diagnosed only when a spontaneous abortion has occurred. There were several cases when the mother managed to bear such a baby, but they all died before reaching and one month old. The mechanisms of gene mutations in the case of triplodia are determined by the complete divergence and non-divergence of all chromosome sets of either female or male germ cells. Also, a double fertilization of one egg can serve as a mechanism. In this case, the placenta degenerates. Such a rebirth is called a cystic skid. As a rule, such changes lead to the development of mental and physiological disorders in the baby, termination of pregnancy.

What gene mutations are associated with a change in the structure of chromosomes

Structural changes in chromosomes are the result of rupture (destruction) of the chromosome. As a result, these chromosomes are connected, violating their former appearance. These modifications can be unbalanced and balanced. Balanced have no excess or lack of material, so they do not appear. They can appear only if there was a gene that is functionally important at the site of the destruction of the chromosome. A balanced set may have unbalanced gametes. As a result, the fertilization of the egg with such a gamete can cause the appearance of a fetus with an unbalanced chromosome set. With such a set, the fetus develops a number of malformations, severe types of pathology appear.

Types of structural modifications

Gene mutations occur at the level of gamete formation. It is impossible to prevent this process, just as it is impossible to know for sure that it can happen. There are several types of structural modifications.

• deletions

This change is associated with the loss of part of the chromosome. After such a break, the chromosome becomes shorter, and its torn off part is lost during further cell division. Interstitial deletions are the case when one chromosome breaks in several places at once. Such chromosomes usually create a non-viable fetus. But there are also cases when babies survived, but because of such a set of chromosomes, they had Wolf-Hirshhorn syndrome, “cat's cry”.

• duplications

These gene mutations occur at the level of organization of doubled DNA sections. Basically, duplication cannot cause such pathologies that cause deletions.

• translocations

Translocation occurs due to the transfer of genetic material from one chromosome to another. If a break occurs simultaneously in several chromosomes and they exchange segments, then this causes a reciprocal translocation. The karyotype of such a translocation has only forty-six chromosomes. The translocation itself is revealed only when detailed analysis and study of the chromosome.

Changing the nucleotide sequence

Gene mutations are associated with a change in the sequence of nucleotides, when they are expressed in a modification of the structures of certain sections of DNA. According to the consequences, such mutations are divided into two types - without a frameshift and with a shift. To know exactly the causes of changes in DNA sections, you need to consider each type separately.

Mutation without frameshift

These gene mutations are associated with the change and replacement of nucleotide pairs in the DNA structure. With such substitutions, DNA length is not lost, but amino acids can be lost and replaced. There is a possibility that the structure of the protein will be preserved, this will serve. Let us consider in detail both variants of development: with and without replacement of amino acids.

Amino acid substitution mutation

Changes in amino acid residues in polypeptides are called missense mutations. There are four chains in the human hemoglobin molecule - two "a" (it is located on the sixteenth chromosome) and two "b" (coding on the eleventh chromosome). If "b" - the chain is normal, and it contains one hundred and forty-six amino acid residues, and the sixth is glutamine, then hemoglobin will be normal. In this case, glutamic acid must be encoded by the GAA triplet. If, due to a mutation, GAA is replaced by GTA, then instead of glutamic acid, valine is formed in the hemoglobin molecule. Thus, instead of normal hemoglobin HbA will appear another hemoglobin HbS. Thus, the replacement of one amino acid and one nucleotide will cause a serious serious illness - sickle cell anemia.

This disease is manifested by the fact that red blood cells become shaped like a sickle. In this form, they are not able to deliver oxygen normally. If on cellular level homozygotes have the formula HbS/HbS, this leads to the death of the child in the very early childhood. If the formula is HbA / HbS, then the erythrocytes have a weak form of change. Such a slight change useful quality- body resistance to malaria. In those countries where there is a danger of contracting malaria the same as in Siberia with a cold, this change has a beneficial quality.

Mutation without amino acid substitution

Nucleotide substitutions without amino acid exchange are called Seimsense mutations. If GAA is replaced by GAG in the DNA region encoding the "b" chain, then due to the fact that it will be in excess, the replacement of glutamic acid cannot occur. The structure of the chain will not be changed, there will be no modifications in the erythrocytes.

Frameshift Mutations

Such gene mutations are associated with a change in the length of DNA. The length can become shorter or longer, depending on the loss or gain of nucleotide pairs. Thus, the entire structure of the protein will be completely changed.

Intragenous suppression may occur. This phenomenon occurs when there is room for two mutations to cancel each other out. This is the moment when a nucleotide pair is added after one has been lost, and vice versa.

Nonsense Mutations

This is special group mutations. It occurs rarely, in its case, the appearance of stop codons. This can happen both with the loss of nucleotide pairs and with their addition. When stop codons appear, polypeptide synthesis stops completely. This can create null alleles. None of the proteins will match this.

There is such a thing as intergenic suppression. This is such a phenomenon when the mutation of some genes suppresses mutations in others.

Are there any changes during pregnancy?

Gene mutations associated with a change in the number of chromosomes can in most cases be identified. To find out if the fetus has malformations and pathologies, screening is prescribed in the first weeks of pregnancy (from ten to thirteen weeks). This is a series of simple examinations: blood sampling from a finger and a vein, ultrasound. On the ultrasound examination the fetus is examined in accordance with the parameters of all limbs, nose and head. These parameters, with a strong non-compliance with the norms, indicate that the baby has developmental defects. This diagnosis is confirmed or refuted based on the results of a blood test.

Also under the close supervision of physicians are expectant mothers, whose babies may develop mutations at the gene level, which are inherited. That is, these are those women in whose relatives there were cases of the birth of a child with mental or physical disabilities identified Down syndrome, Patau and other genetic diseases.

Mutation is understood change in the amount and structure of DNA in a cell or in an organism. In other words, mutation is a change in the genotype. A feature of the genotype change is that this change as a result of mitosis or meiosis can be transferred to the next generations of cells.

Most often, mutations are understood as a small change in the sequence of DNA nucleotides (changes in one gene). These are the so-called. However, in addition to them, there are also when changes affect large sections of DNA, or the number of chromosomes changes.

As a result of a mutation, a new trait may suddenly appear in an organism.

The idea that it is mutation that is the cause of the appearance of new traits transmitted through generations was first expressed by Hugh de Vries in 1901. Later, mutations in Drosophila were studied by T. Morgan and the staff of his school.

Mutation - harm or benefit?

Mutations that occur in "insignificant" ("silent") sections of DNA do not change the characteristics of the organism and can be easily passed on from generation to generation (natural selection will not act on them). Such mutations can be considered neutral. Mutations are also neutral when a gene segment is replaced with a synonymous one. In this case, although the sequence of nucleotides in a certain area will be different, the same protein will be synthesized (with the same amino acid sequence).

However, a mutation can affect a significant gene, change the amino acid sequence of the synthesized protein, and, consequently, cause a change in the characteristics of the organism. Subsequently, if the concentration of a mutation in a population reaches a certain level, this will lead to a change characteristic feature the entire population.

In wildlife, mutations occur as errors in DNA, so all of them are a priori harmful. Most mutations reduce the viability of the organism, cause various diseases. Mutations that occur in somatic cells are not transmitted to the next generation, but as a result of mitosis, daughter cells are formed that make up one or another tissue. Often, somatic mutations lead to the formation of various tumors and other diseases.

Mutations that occur in germ cells can be passed on to the next generation. In stable conditions external environment almost all genotypic changes are harmful. But if environmental conditions change, it may turn out that a previously harmful mutation will become beneficial.

For example, a mutation that causes the formation of short wings in some insect is likely to be harmful in a population living in places where there is no strong wind. This mutation will be akin to deformity, disease. Insects with it will have difficulty finding mating partners. But if stronger winds begin to blow on the terrain (for example, a forest area was destroyed as a result of a fire), then insects with long wings will be blown away by the wind, it will be harder for them to move. Under such conditions, short-winged individuals can gain an advantage. They will find partners and food more often than long-winged ones. After some time, there will be more short-winged mutants in the population. Thus, the mutation will be fixed and become the norm.

Mutations underlie natural selection and this is their main benefit. For the body, the overwhelming number of mutations is harmful.

Why do mutations occur?

In nature, mutations occur randomly and spontaneously. That is, any gene can mutate at any time. However, the mutation rate in different organisms and cells are different. For example, it is related to the duration life cycle: the shorter it is, the more mutations occur. Thus, mutations occur much more frequently in bacteria than in eukaryotic organisms.

Except spontaneous mutations(occurring in vivo) are induced(by a person in laboratory conditions or adverse environmental conditions) mutations.

Basically, mutations occur as a result of errors in DNA replication (doubling), repair (restoration) of DNA, with unequal crossing over, improper chromosome segregation in meiosis, etc.

So in the cells there is a constant recovery (repair) damaged areas DNA. However, if as a result various reasons repair mechanisms are violated, then errors in the DNA will remain and accumulate.

The result of a replication error is the replacement of one nucleotide in the DNA chain with another.

What causes mutations?

Increased levels of mutations cause x-rays, ultraviolet and gamma rays. Also, mutagens include α- and β-particles, neutrons, cosmic radiation (all these are high-energy particles).

Mutagen is something that can cause mutation.

In addition to various radiations, many chemical substances: formaldehyde, colchicine, tobacco components, pesticides, preservatives, some medications and etc.

Mutations are changes in the DNA of a cell. Occurs under the influence of ultraviolet radiation ( x-rays) etc. They are inherited and serve as material for natural selection.

Gene mutations- change in the structure of one gene. This is a change in the sequence of nucleotides: dropout, insertion, replacement, etc. For example, replacing A with T. Causes - violations during doubling (replication) of DNA. Examples: sickle cell anemia, phenylketonuria.

Chromosomal mutations- change in the structure of chromosomes: loss of a site, doubling of a site, rotation of a site by 180 degrees, transfer of a site to another (non-homologous) chromosome, etc. Causes - violations during crossing over. Example: cat cry syndrome.

Genomic mutations- change in the number of chromosomes. Causes - violations in the divergence of chromosomes.

• Polyploidy- multiple changes (several times, for example, 12 → 24). It does not occur in animals, in plants it leads to an increase in size.
• Aneuploidy- changes on one or two chromosomes. For example, one extra twenty-first chromosome leads to Down syndrome (with total chromosomes - 47).

Cytoplasmic mutations- changes in the DNA of mitochondria and plastids. They are transmitted only through the female line, because. mitochondria and plastids from spermatozoa do not enter the zygote. An example in plants is variegation.

Somatic- mutations in somatic cells (cells of the body; there may be four of the above types). During sexual reproduction, they are not inherited. They are transmitted during vegetative propagation in plants, during budding and fragmentation in coelenterates (in hydra).

The following terms, except for two, are used to describe the consequences of a violation of the arrangement of nucleotides in a DNA region that controls protein synthesis. Define these two concepts, "falling out" of general list, and write down the numbers under which they are indicated.
1) violation of the primary structure of the polypeptide
2) divergence of chromosomes
3) change in protein functions
4) gene mutation
5) crossing over

Answer

Choose the one most correct option. Polyploid organisms result from
1) genomic mutations

3) gene mutations
4) combinative variability

Answer

Establish a correspondence between the characteristic of variability and its type: 1) cytoplasmic, 2) combinative
A) occurs with independent divergence of chromosomes in meiosis
B) occurs as a result of mutations in the DNA of mitochondria
B) occurs as a result of chromosome crossing
D) manifested as a result of mutations in plastid DNA
D) occurs when chance meeting gametes

Answer

Choose one, the most correct option. Down syndrome is the result of a mutation
1) genomic
2) cytoplasmic
3) chromosomal
4) recessive

Answer

1. Establish a correspondence between the characteristic of a mutation and its type: 1) gene, 2) chromosomal, 3) genomic
A) a change in the sequence of nucleotides in a DNA molecule
B) a change in the structure of chromosomes
C) change in the number of chromosomes in the nucleus
D) polyploidy
E) change in the sequence of genes

Answer

2. Establish a correspondence between the characteristics and types of mutations: 1) gene, 2) genomic, 3) chromosomal. Write down the numbers 1-3 in the order corresponding to the letters.
A) deletion of a segment of a chromosome
B) a change in the sequence of nucleotides in a DNA molecule
C) a multiple increase in the haploid set of chromosomes
D) aneuploidy
E) change in the sequence of genes in the chromosome
E) loss of one nucleotide

Answer

Choose three options. What is a genomic mutation characterized by?
1) a change in the nucleotide sequence of DNA
2) loss of one chromosome in the diploid set
3) a multiple increase in the number of chromosomes
4) a change in the structure of synthesized proteins
5) doubling a section of a chromosome
6) a change in the number of chromosomes in the karyotype

Answer

1. Below is a list of characteristics of variability. All but two of them are used to describe the characteristics of genomic variability. Find two characteristics that "drop out" of the general series, and write down the numbers under which they are indicated.
1) limited by the norm of the reaction of the sign
2) the number of chromosomes is increased and a multiple of haploid
3) an additional X chromosome appears
4) has a group character
5) there is a loss of the Y chromosome

Answer

2. All but two of the characteristics below are used to describe genomic mutations. Identify two characteristics that “fall out” of the general list, and write down the numbers under which they are indicated.
1) discrepancy violation homologous chromosomes during cell division
2) destruction of the fission spindle
3) conjugation of homologous chromosomes
4) change in the number of chromosomes
5) an increase in the number of nucleotides in genes

Answer

3. All but two of the characteristics below are used to describe genomic mutations. Identify two characteristics that “fall out” of the general list, and write down the numbers under which they are indicated.
1) change in the sequence of nucleotides in a DNA molecule
2) a multiple increase in the chromosome set
3) decrease in the number of chromosomes
4) duplication of a chromosome segment
5) nondisjunction of homologous chromosomes

Answer

Choose one, the most correct option. Recessive gene mutations change
1) the sequence of stages of individual development
2) composition of triplets in a DNA segment
3) a set of chromosomes in somatic cells
4) the structure of autosomes

Answer

Choose one, the most correct option. Cytoplasmic variability is associated with the fact that
1) meiotic division is disturbed
2) mitochondrial DNA is able to mutate
3) new alleles appear in autosomes
4) gametes are formed that are incapable of fertilization

Answer

1. Below is a list of characteristics of variability. All but two of them are used to describe the characteristics of chromosomal variation. Find two characteristics that "drop out" of the general series, and write down the numbers under which they are indicated.
1) loss of a chromosome segment
2) rotation of a chromosome segment by 180 degrees
3) decrease in the number of chromosomes in the karyotype
4) the appearance of an additional X chromosome
5) transfer of a chromosome segment to a non-homologous chromosome

Answer

2. All but two of the following features are used to describe a chromosomal mutation. Identify two terms that "fall out" from the general list, and write down the numbers under which they are indicated.
1) the number of chromosomes increased by 1-2
2) one nucleotide in DNA is replaced by another
3) a section of one chromosome is transferred to another
4) there was a loss of a section of the chromosome
5) a segment of the chromosome is turned 180°

Answer

3. All but two of the characteristics below are used to describe chromosomal variation. Find two characteristics that "drop out" of the general series, and write down the numbers under which they are indicated.
1) multiplication of a segment of a chromosome several times
2) the appearance of an additional autosome
3) change in the nucleotide sequence
4) loss of the terminal section of the chromosome
5) turn of the gene in the chromosome by 180 degrees

Answer

Choose one, the most correct option. What type of mutation is a change in the structure of DNA in mitochondria
1) genomic
2) chromosomal
3) cytoplasmic
4) combinative

Answer

Choose one, the most correct option. The variegation of the nocturnal beauty and snapdragon is determined by variability
1) combinative
2) chromosomal
3) cytoplasmic
4) genetic

Answer

1. Below is a list of characteristics of variability. All but two of them are used to describe the characteristics of genetic variation. Find two characteristics that "drop out" of the general series, and write down the numbers under which they are indicated.
1) due to the combination of gametes during fertilization
2) due to a change in the sequence of nucleotides in the triplet
3) is formed during the recombination of genes during crossing over
4) characterized by changes within the gene
5) is formed when the nucleotide sequence changes

Answer

2. All of the following characteristics, except for two, are the causes of gene mutation. Define these two concepts that “fall out” from the general list, and write down the numbers under which they are indicated.
1) conjugation of homologous chromosomes and exchange of genes between them
2) replacement of one nucleotide in DNA with another
3) change in the sequence of the connection of nucleotides
4) the appearance of an extra chromosome in the genotype
5) loss of one triplet in the DNA region encoding the primary structure of the protein

Answer

3. All but two of the characteristics below are used to describe gene mutations. Identify two characteristics that “fall out” of the general list, and write down the numbers under which they are indicated.
1) replacement of a pair of nucleotides
2) the occurrence of a stop codon within the gene
3) doubling the number of individual nucleotides in DNA
4) an increase in the number of chromosomes
5) loss of a chromosome segment

Answer

4. All but two of the characteristics below are used to describe gene mutations. Identify two characteristics that “fall out” of the general list, and write down the numbers under which they are indicated.
1) adding one triplet to DNA
2) an increase in the number of autosomes
3) change in the sequence of nucleotides in DNA
4) loss of individual nucleotides in DNA
5) multiple increase in the number of chromosomes

Answer

5. All of the following characteristics, except for two, are typical for gene mutations. Identify two characteristics that “fall out” of the general list, and write down the numbers under which they are indicated.
1) the emergence of polyploid forms
2) random doubling of nucleotides in the gene
3) loss of one triplet in the process of replication
4) the formation of new alleles of one gene
5) violation of the divergence of homologous chromosomes in meiosis

Answer

Choose one, the most correct option. Polyploid wheat varieties are the result of variability
1) chromosomal
2) modification
3) gene
4) genomic

Answer

Choose one, the most correct option. The production of polyploid wheat varieties by breeders is possible due to the mutation
1) cytoplasmic
2) gene
3) chromosomal
4) genomic

Answer

Establish a correspondence between characteristics and mutations: 1) genomic, 2) chromosomal. Write the numbers 1 and 2 in the correct order.
A) a multiple increase in the number of chromosomes
B) rotation of a segment of the chromosome by 180 degrees
C) exchange of sections of non-homologous chromosomes
D) loss of the central region of the chromosome
D) duplication of a section of a chromosome
E) repeated change in the number of chromosomes

Answer

Choose one, the most correct option. The appearance of different alleles of one gene occurs as a result of
1) indirect cell division
2) modification variability
3) mutation process
4) combinative variability

Answer

All but two of the terms listed below are used to classify mutations by changes in genetic material. Identify two terms that "fall out" from the general list, and write down the numbers under which they are indicated.
1) genomic
2) generative
3) chromosomal
4) spontaneous
5) gene

Answer

Establish a correspondence between the types of mutations and their characteristics and examples: 1) genomic, 2) chromosomal. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) loss or appearance of extra chromosomes as a result of a violation of meiosis
B) lead to disruption of the functioning of the gene
C) an example is polyploidy in protozoa and plants
D) doubling or loss of a chromosome segment
D) a prime example is Down syndrome

Answer

Establish a correspondence between the categories of hereditary diseases and their examples: 1) gene, 2) chromosomal. Write down the numbers 1 and 2 in the order corresponding to the letters.
A) hemophilia
B) albinism
B) colorblindness
D) "cat's cry" syndrome
D) phenylketonuria

Answer

Find three errors in the given text and indicate the numbers of sentences with errors.(1) Mutations are accidental permanent change genotype. (2) Gene mutations are the result of "mistakes" that occur in the process of doubling DNA molecules. (3) Mutations are called genomic, which lead to a change in the structure of chromosomes. (4) Many cultivated plants are polyploids. (5) Polyploid cells contain one to three extra chromosomes. (6) Polyploid plants are characterized by stronger growth and larger size. (7) Polyploidy is widely used in both plant breeding and animal breeding.

Answer

Analyze the table "Types of variability". For each cell marked with a letter, select the appropriate concept or the appropriate example from the list provided.
1) somatic
2) gene
3) replacement of one nucleotide with another
4) duplication of a gene in a region of the chromosome
5) addition or loss of nucleotides
6) hemophilia
7) color blindness
8) trisomy in the chromosome set

Answer

© D.V. Pozdnyakov, 2009-2019

Hello, this is Olga Ryshkova. Today we will talk about mutations. What is a mutation? Mutations in human organisms Is it good or bad, is it a positive or dangerous phenomenon for us? Mutations can cause diseases, or they can give their carriers immunity to diseases such as cancer, AIDS, malaria, and diabetes.

What is a mutation?

What is a mutation and where does it occur? Human cells (like plants and animals) have a nucleus.

The nucleus contains a set of chromosomes. A chromosome is a carrier of genes, that is, a carrier of genetic, hereditary information.

Each chromosome is formed from a DNA molecule that contains genetic information and is passed from parents to children. The DNA molecule looks like this:

Mutations occur in the DNA molecule.

How do they happen?

How do mutations happen? The DNA of each person consists of only four nitrogenous bases - A, T, G, C. But the DNA molecule is very large and they are repeated many times in it in different sequences. The characteristics of each of our cells depends on the sequence in which these nitrogenous bases are located.

Changing the sequence of these bases in DNA leads to mutations.

A mutation can be caused by a small change in one DNA base or part of it. Part of the chromosome may be lost. Or this part can be duplicated. Or two genes are swapped. Mutations occur when there is confusion in the genes. A gene is a section of DNA. In this figure, for clarity, the letters indicate not the nitrogenous bases (there are only four of them - A, T, G, C), but the parts of the chromosome with which changes occur.

But it's not a mutation.

You noticed that I said "leads to mutations" and not "this is a mutation." For example, a change has occurred in DNA, and the cell in which this DNA is located can simply die. And there will be no consequences in the body. In order for us to say that a mutation has occurred, the change must be persistent. This means that the cell will divide, the daughter cells will divide again and so many times, and this change will be transmitted to all the descendants of this cell and will be fixed in the body. That's when we can say that a mutation has occurred, that is, a change in the human genome and this change can be passed on to his descendants.

Why are they happening?

Why do mutations occur in human cells? There is such a thing as "mutagens", these are physical and chemical factors that cause changes in the structure of chromosomes and genes, that is, they cause mutations.

• The physical ones include radiation, ionizing and ultraviolet radiation, high and low temperatures.
• To chemical - nitrates, pesticides, petroleum products, some nutritional supplements, some drugs, etc.
• Mutagens can be biological, such as some microorganisms, viruses (measles, rubella, influenza), as well as fat oxidation products inside the human body.

Mutations can be dangerous.

Even the smallest gene mutation dramatically increases the likelihood birth defects. Mutations can cause abnormalities in the development of the fetus. They occur during fertilization, when the sperm meets the egg. Something might go wrong when mixing genomes, or the problem might already be present in the parent's genes. This leads to the birth of children with genetic abnormalities.

Mutations can be beneficial.

To some, these mutations give an attractive appearance, high level intelligence or athletic physique. Such mutations effectively attract the opposite sex. Demanded mutated genes are passed on to descendants and spread across the planet.

Mutations have led to a large number people immune to dangerous infectious diseases, such as plague and AIDS, these people will not get sick with them even during the most terrible epidemic.

Mutations are beneficial and harmful at the same time.

One of the major diseases in Africa is malaria. But there are people who do not get malaria. These are people with sickle-shaped red blood cells, like this:

Mutated erythrocytes were inherited from their ancestors. Such red blood cells do not tolerate oxygen well, so their owners are frail and suffer from anemia. But they are immune to malaria.

Or other great example. genetic mutation, hereditary disease- Laron's syndrome. These people have a hereditary deficiency of the insulin-like growth factor IGF-1, because of this, their growth stops very early. But due to the lack of IGF-1, they never get cancer, cardiovascular disease and diabetes. Among people with Laron's syndrome, these diseases do not occur at all.

The foods we eat are mutants.

Yes, mutants, and those were beneficial mutations. Most of The foods we eat are the result of mutations.

Two examples. Wild rice is red, its yield is 20% lower than that of sowing rice. Sown rice appeared as a mutated form about 10,000 years ago. It turned out that it is easier to clean, cook faster, which allowed people to save fuel. Due to the high yield and useful properties the peasants began to prefer the mutated species. That is, white rice is mutated red.

The wheat that we eat now began to be grown 7,000 years before our era. The man chose mutated wild wheat with larger and non-shattering grains. We are still growing it.

Other cultivated plants have also been grown for several thousand years. Man selected mutated varieties of wild plants and specially cultivated them. Today we consume the results of mutations selected in ancient times.

Not all mutations are inherited.

I'm talking about mutations that occur during the life of one person. These are cancer cells.

In the next article I will tell you about how mutations lead to the appearance cancer cells and where did people among us come from who are immune to HIV infection, people who are immune to HIV.

If you still have questions about what mutations are, where, how and why they occur, we will discuss this in the comments. If the article seemed useful to you, share it with your friends on social networks.

Mutations are called spontaneous changes in the DNA structure of living organisms, leading to the occurrence of all kinds of abnormalities in growth and development. So, let's consider what a mutation is, the reasons for its occurrence and those that exist in it. It is also worth paying attention to the impact of genotype changes on nature.

Scientists say that mutations have always existed and are present in the organisms of absolutely all living beings on the planet, moreover, up to several hundred of them can be observed in one organism. Their manifestation and the degree of severity depend on what causes they were provoked and which genetic chain was affected.

Causes of Mutations

The causes of mutations can be very diverse, and they can occur not only naturally but also artificially in the laboratory. Genetic scientists identify the following factors for the occurrence of changes:

2) gene mutations - changes in the sequence of nucleotide construction during the formation of new DNA chains (phenylketonuria).

The meaning of mutations

In most cases, they harm the entire body, because they interfere with its normal growth and development, and sometimes lead to death. Beneficial Mutations never meet, even if they give superpowers. They become the basis for active action and influence the selection of living organisms, leading to the emergence of new species or degeneration. Thus, answering the question: "What is a mutation?" - it is worth noting that these are the slightest changes in the structure of DNA that disrupt the development and vital activity of the whole organism.