Factors leading to mutation. Mutagenesis. Mutagenic factors Mutations that are artificially caused by the action of certain factors

When changes in DNA occur spontaneously, causing various pathologies of development and growth in living organisms, they speak of mutations. To understand their essence, it is necessary to learn more about the reasons leading to them.

Geneticists claim that mutations are characteristic of all organisms on the planet without exception (living ones) and that they have existed forever, and one organism can have several hundred of them. However, they differ in the degree of severity and nature of manifestation, which are determined by the factors that provoke them, as well as the affected gene chain.

They can be natural and artificial, i.e. caused in laboratory conditions.

The most common factors leading to such changes from the point of view of geneticists are the following:

ionizing radiation and x-rays. When affecting the body, radioactive radiation is accompanied by a change in the electron charge in the atoms. This causes a disruption in the normal course of physico-chemical and chemical-biological processes;

very high temperatures often cause changes when the sensitivity threshold of a particular individual is exceeded;

when cells divide, delays may occur, as well as their proliferation too quickly, which also becomes an impetus for negative changes;

“defects” that occur in DNA, in which it is not possible to return the atom to its original state even after restoration.

Varieties

At the moment, more than thirty types of deviations in the gene pool of a living organism and genotype are known that cause mutations. Some are quite safe and do not manifest themselves in any way externally, i.e. do not lead to internal and external deformities, so the living organism does not feel discomfort. Others, on the contrary, are accompanied by severe discomfort.

To understand what mutations are, you should familiarize yourself with the mutagenic classification, grouped according to the causes of defects:

genetic and somatic, differing in the typology of cells that have undergone changes. Somatic is characteristic of mammalian cells. They can be passed on solely by inheritance (for example, different eye colors). Its formation occurs in the mother's womb. Genetic mutation is common in plants and invertebrates. It is caused by negative environmental factors. An example of a manifestation is mushrooms appearing on trees, etc.;

nuclear refer to mutations based on the location of the cells that have undergone changes. Such options cannot be treated, since the DNA itself is directly affected. The second type of mutation is cytoplasmic (or atavism). It affects any fluids that interact with the cell nucleus and the cells themselves. Such mutations are treatable;

explicit (natural) and induced (artificial). The first appears suddenly and for no apparent reason. The latter are associated with the failure of physical or chemical processes;

gene and genomic, differing in their severity. In the first variant, the changes concern disorders that change the sequence of nucleotide structure in newly formed DNA chains (phenylketonuria can be considered as an example).

In the second case, there is a change in the quantitative chromosome set, and the example is Down's disease, Konovalov-Wilson's disease, etc.

Meaning

The harm of mutations to the body is undeniable, since it not only affects its normal development, but often leads to death. Mutations cannot be beneficial. This also applies to cases of superpowers. They are always prerequisites for natural selection, leading to the emergence of new species of organisms (living) or to complete extinction.

It is now clear that processes that affect the structure of DNA, leading to minor or fatal disorders, affect the normal development and functioning of the body.

Factors that cause mutations are called mutagenic factors (mutagens) and are divided into:

1. Physical;

2. Chemical;

3. Biological.

To physical mutagenic factors include various types of radiation, temperature, humidity, etc. The most powerful mutagenic effect is exerted by ionizing radiation - x-rays, α-, β-, γ-rays. They have great penetrating power.

When they act on the body they cause:

a) ionization of tissues - the formation of free radicals (OH) or (H) from water located in tissues. These ions enter into a chemical interaction with DNA, break down nucleic acid and other organic substances;

b) ultraviolet radiation is characterized by lower energy, penetrates only through the superficial layers of the skin and does not cause ionization of tissues, but leads to the formation of dimers (chemical bonds between two pyrimidine bases of the same chain, often T-T). The presence of dimers in DNA leads to errors during its replication and disrupts the reading of genetic information;

c) rupture of spindle filaments;

d) disruption of the structure of genes and chromosomes, i.e. formation of gene and chromosomal mutations.

Chemical mutagens include:

Natural organic and inorganic substances (nitrites, nitrates, alkaloids, hormones, enzymes, etc.);

Synthetic substances not previously found in nature (pesticides, insecticides, food preservatives, medicinal substances).

Products of industrial processing of natural compounds - coal, oil.

Mechanisms of their action :

a) deamination - the removal of an amino group from an amino acid molecule;

b) suppression of nucleic acid synthesis;

c) replacement of nitrogenous bases with their analogues.

Chemical mutagens cause predominantly gene mutations and act during DNA replication.

Biological mutagens include:

Viruses (influenza, rubella, measles)

Mechanisms of their action:

a) viruses integrate their DNA into the DNA of host cells.

Biological mutagens cause gene and chromosomal mutations.

End of work -

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Biology
course of lectures for students studying in Russian Ryazan

Biology
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Definition and forms of variability
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Stability and repair of genetic material
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Twin research method
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Ontogenetic method
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Simulation method
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Immunological research method
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Biochemical method
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Mutagenic factors – factors causing mutation.

Factors of physical, chemical and biological nature have a mutagenic effect.

Chemical substances that cause mutations include organic and inorganic substances, such as acids, alkalis, peroxides, metal salts, formaldehyde, pesticides, defoliants, herbicides, colchicine, etc.

The action of chemical factors: enhance mutation processes, cause point mutations that induce chromosomal rearrangements, and cause disruption of DNA replication. Some mutagens can cause disruption of meiosis, which leads to chromosome non-disjunction.

Physical factors: ionizing radiation, radioactive decay, ultraviolet radiation, electromagnetic radiation, extreme heat and cold.

The action of physical factors: X-ray radiation, having a high penetrating ability, causes the formation of free radicals of water, which break down nucleic acids, causing gene and chromosomal rearrangements. Ultraviolet radiation leads to the formation of thymidine dimers, which cause disruption of DNA replication.

Biological factors: viruses (measles, rubella, influenza), metabolic products (lipid oxidation products), microorganism antigens./

The action of biological factors: they increase the rate of cell mutations by suppressing the activity of repair systems.

3. Gene and chromosomal mutations, their characteristics.

Gene (point) mutations- these are changes in the number and/or sequence of nucleotides in the DNA structure (insertions, deletions, movements, substitutions of nucleotides) within individual genes, leading to a change in the quantity or quality of the corresponding protein products. Base substitutions lead to the appearance of three types of mutant codons: with a changed meaning (missense mutations), with an unchanged meaning (neutral mutations) and meaningless or stop codons (nonsense mutations).

There are three groups of such changes. Mutations of the first group consist of replacing some bases with others (about 20% of spontaneously occurring gene changes). The second group of mutations is caused by a shift in the reading frame that occurs when the number of nucleotide pairs in the gene changes. The third group is mutations associated with a change in the order of nucleotide sequences within a gene.

Mutations by type of replacement of nitrogenous bases occur due to the following reasons. Firstly, a change in the structure of a base already included in the DNA helix can occur accidentally or under the influence of chemical agents. If such an altered form of the base remains undetected by repair enzymes, then during the next replication cycle it can attach another nucleotide to itself.

Another reason for base substitution may be the erroneous inclusion in the synthesized DNA chain of a nucleotide carrying a chemically altered form of the base or its analogue. Thus, a change in DNA structure by base substitution occurs before or during replication, initially in one polynucleotide chain. If such changes are not corrected during repair, then during subsequent replication they become the property of both DNA strands. The consequence of replacing one pair of complementary nucleotides with another is the formation of a new triplet in the DNA nucleotide sequence, different from the previous one. In this case, the new triplet can encode the same amino acid (a “synonym” triplet), another amino acid, or not encode any amino acid (a nonsense triplet). In the first case, no changes occur, in the second, the structure and properties of the corresponding protein change. Depending on the nature and location of the replacement that occurs, the specific properties of the protein change to varying degrees, in some cases significantly. It is known that replacing nucleotides in one triplet leads to the formation of synonymous triplets in 25% of cases, meaningless triplets in 2-3%, and true gene mutations in 75-70% of cases.

Chromosomal mutations(or aberrations) – changes in the structure of chromosomes. At the chromosomal level of organization, the hereditary material has all the characteristics of the substrate of heredity and variability, including the ability to acquire changes that can be transmitted to a new generation. Under the influence of various influences, the physicochemical and morphological structure of chromosomes can change. Changes in the structure of chromosomes, as a rule, are based on an initial violation of its integrity - breaks, which are accompanied by various rearrangements, called chromosomal mutations or aberrations. Chromosome breaks occur naturally during crossing over, when they are accompanied by the exchange of corresponding sections between homologous chromosomes. Crossing-over disruption, in which chromosomes exchange unequal genetic material, leads to the appearance of new linkage groups, where individual sections fall out - deletion - or double - duplication. With such rearrangements, the number of genes in the linkage group changes. Chromosome breaks can also occur under the influence of various external factors, most often physical (for example, ionizing radiation), certain chemical compounds, and viruses. Violation of the integrity of chromosomes can be accompanied by a rotation of its section located between the breaks by 180° - inversion. A fragment of a chromosome separated from it during a break can attach to another chromosome - translocation. Often, two damaged non-homologous chromosomes mutually exchange detached sections - reciprocal translocation. It is possible to attach a fragment to its own chromosome, but in another place - transposition. A special category of chromosomal mutations are aberrations associated with the fusion or separation of chromosomes, when two non-homologous structures combine into one - Robertsonian translocation, or one chromosome forms two independent chromosomes. With such mutations, not only the morphology of chromosomes changes, but also their number in the karyotype changes. The latter can be considered a genomic mutation. The cause of genomic mutations can also be a disruption of the processes occurring in meiosis. Violation of the divergence of bivalents in anaphase leads to the appearance of gametes with different numbers of chromosomes. Fertilization of such gametes by normal germ cells leads to a change in the total number of chromosomes in the karyotype due to a decrease (monosomy) or increase (trisomy) in the number of individual chromosomes. Such violations of the genome structure are called aneuploidy. If the mechanism of distribution of homologous chromosomes is damaged, the cell remains undivided, and then diploid gametes are formed. Fertilization of such gametes leads to the formation of triploid zygotes, that is, an increase in the number of sets of chromosomes occurs - polyploidy. Any mutational changes in the hereditary material of gametes - generative mutations - become the property of the next generation if such gametes are involved in fertilization.

There are many inherited metabolic diseases. Examples include disorders of porphyrin metabolism (Gunther's disease, erythropoietic protoporphyria, coproporphyria, etc.). These are diseases that manifest themselves after exposure to UV rays by damage to the skin and deeper tissues, an increased content of proporphins and coproporphyrins in erythrocytes. They appear among brothers and sisters of the same generation.

Factors causing mutations. Factors that cause (induce) mutations can be a wide variety of environmental influences: temperature, ultraviolet radiation, radiation (both natural and artificial), the effects of various chemical compounds - mutagens. Mutagens are agents of the external environment that cause certain changes in the genotype - mutation, and the process of formation of mutations itself - mutagenesis.

Radioactive mutagenesis began to be studied in the 20s of our century. In 1925, Soviet scientists G.S. Filippov and G.A. Nadson, for the first time in the history of genetics, used X-rays to obtain mutations in yeast. A year later, the American researcher G. Meller (later twice a Nobel Prize winner), who worked for a long time in Moscow at the institute headed by N.K. Koltsov, used the same mutagen on Drosophila.

Chemical mutagenesis was first purposefully studied by N.K. Koltsov’s collaborator V.V. Sakharov in 1931 on Drosophila when its eggs were exposed to iodine, and later by M.E. Lobashov.

Chemical mutagens include a wide variety of substances (alkylating compounds, hydrogen peroxide, aldehydes and ketones, nitric acid and its analogs, various antimetabolites, salts of heavy metals, dyes with basic properties, aromatic substances), insecticides (from the Latin insecta - insects , cida - killer), herbicides (then lat. herba - grass), drugs, alcohol, nicotine, some medicinal substances and many others.

Genetically active factors can be divided into 3 categories: physical, chemical and biological.

Physical factors. These include various types of ionizing radiation and ultraviolet radiation. A study of the effect of radiation on the mutation process showed that in this case there is no threshold dose, and even the smallest doses increase the likelihood of mutations occurring in the population. An increase in the frequency of mutations is dangerous not so much in an individual sense, but from the point of view of increasing the genetic load of the population. For example, irradiation of one of the spouses with a dose within the range of doubling the frequency of mutations (1.0 - 1.5 Gy) slightly increases the risk of having a sick child (from a level of 4 - 5% to a level of 5 - 6%). If the population of an entire region receives the same dose, the number of hereditary diseases in the population will double in a generation.

Chemical factors. The chemicalization of agriculture and other areas of human activity, the development of the chemical industry led to the synthesis of a huge flow of substances (totaling from 3.5 to 4.3 million), including those that had never existed in the biosphere for millions of years of previous evolution. This means, first of all, the indegradability and thus long-term preservation of foreign substances entering the environment.

What was initially taken as an achievement in the fight against pests later turned into a complex problem. Widely used in the 40s - 60s insecticide DDT, which belongs to the class of chlorinated hydrocarbons, led to its spread throughout the globe, right up to the ice of Antarctica.

Most pesticides are highly resistant to chemical and biological degradation and have a high level of toxicity. anthropogenetics chromosomal inheritance anomaly

Biological factors. Along with physical and chemical mutagens, some factors of biological nature also have genetic activity. The mechanisms of the mutagenic effect of these factors have been studied in the least detail. At the end of the 30s, S. and M. Gershenzon began research on mutagenesis in Drosophila under the influence of exogenous DNA and viruses. Since then, the mutagenic effect of many viral infections in humans has been established. Chromosome aberrations in somatic cells cause smallpox, measles, chickenpox, mumps, influenza, hepatitis viruses and etc.

Factors causing mutations. Factors that cause (induce) mutations can be a wide variety of environmental influences: temperature, ultraviolet radiation, radiation (both natural and artificial), the actions of various chemical compounds - mutagens. Mutagens are agents of the external environment that cause certain changes in the genotype - mutation, and the process of formation of mutations is called mutagenesis.

Radioactive mutagenesis began to be studied in the 20s of our century. In 1925, Soviet scientists G.S. Filippov and G.A. Nadson, for the first time in the history of genetics, used X-rays to obtain mutations in yeast. A year later, the American researcher G. Meller (later twice a Nobel Prize winner), who worked for a long time in Moscow at the institute headed by N.K. Koltsov, used the same mutagen on Drosophila.

Chemical mutagenesis was first purposefully studied by N.K. Koltsov’s collaborator V.V. Sakharov in 1931 on Drosophila when its eggs were exposed to iodine, and later by M.E. Lobashov.

Chemical mutagens include a wide variety of substances (alkylating compounds, hydrogen peroxide, aldehydes and ketones, nitric acid and its analogues, various antimetabolites, salts of heavy metals, dyes with basic properties, aromatic substances), insecticides (from the Latin insecta - insects , cida - killer), herbicides (then lat. herba - grass), drugs, alcohol, nicotine, some medicinal substances and many others.

Genetically active factors can be divided into 3 categories: physical, chemical and biological.

Physical factors. These include various types of ionizing radiation and ultraviolet radiation. A study of the effect of radiation on the mutation process showed that in this case there is no threshold dose, and even the smallest doses increase the likelihood of mutations occurring in the population. An increase in the frequency of mutations is dangerous not so much in an individual sense, but from the point of view of increasing the genetic load of the population. For example, irradiation of one of the spouses with a dose within the range of doubling the frequency of mutations (1.0 - 1.5 Gy) slightly increases the risk of having a sick child (from a level of 4 - 5% to a level of 5 - 6%). If the population of an entire region receives the same dose, the number of hereditary diseases in the population will double in a generation.

Chemical factors. The chemicalization of agriculture and other areas of human activity, the development of the chemical industry led to the synthesis of a huge flow of substances (totaling from 3.5 to 4.3 million), including those that had never existed in the biosphere for millions of years of previous evolution. This means, first of all, the indegradability and thus long-term preservation of foreign substances entering the environment. What was initially taken as an achievement in the fight against pests later turned into a complex problem. The widespread use in the 40-60s of the insecticide DDT, which belongs to the class of chlorinated hydrocarbons, led to its spread throughout the globe, right up to the ice of Antarctica.

Most pesticides are highly resistant to chemical and biological degradation and have a high level of toxicity.

Biological factors. Along with physical and chemical mutagens, some factors of biological nature also have genetic activity. The mechanisms of the mutagenic effect of these factors have been studied in the least detail. At the end of the 30s, S. and M. Gershenzon began research on mutagenesis in Drosophila under the influence of exogenous DNA and viruses. Since then, the mutagenic effect of many viral infections in humans has been established. Chromosome aberrations in somatic cells are caused by smallpox, measles, chickenpox, mumps, influenza, hepatitis viruses, etc.

More on the topic Factors causing mutations of the hereditary apparatus:

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