Mutational variability. Basic provisions of mutation theory

Mutation theory

Mutation theory or mutation theory- a branch of genetics that lays the foundations of genetic variability and evolution.

Emergence

Mutation theory is one of the foundations of genetics. It originated shortly after the rediscovery of Mendel's laws by T. Morgan at the beginning of the 20th century. It can be considered that it almost simultaneously arose in the minds of the Dutchman De Vries (1903) and the domestic botanist S.I. Korzhinsky (1899). However, the priority in primacy and in greater coincidence of the original provisions belongs to the Russian scientist. The recognition of the main evolutionary significance of discrete variability and the denial of the role of natural selection in the theories of Korzhinsky and De Vries was associated with the intractability at that time of the contradiction in the evolutionary teachings of Charles Darwin between the important role of small deviations and their “absorption” during crossings (see Jenkin’s nightmare) .

Basic provisions

The main provisions of the Korzhinsky-De Vries mutation theory can be reduced to the following points:

1. Mutations are sudden, like discrete changes in traits
2. New forms are stable
3. Unlike non-hereditary changes, mutations do not form continuous series and are not grouped around any average type. They represent qualitative leaps in change
4. Mutations manifest themselves in different ways and can be either beneficial or harmful.
5. The probability of detecting mutations depends on the number of individuals studied
6. Similar mutations can occur repeatedly

Research by H. De Vries was carried out on various species of Oenothera, which during the experiment did not produce mutations, but showed complex combinative variability, since these forms were complex heterozygotes for translocations.

Strict proof of the occurrence of mutations belongs to V. Johannsen based on experiments on self-pollinating lines of beans and barley - seed masses were studied, mutational changes in this trait were discovered by V. Johannsen (1908-1913). It is noteworthy that even having a mutational nature, the mass of seeds was distributed relative to certain average values, thereby casting doubt on the third point of the mutation theory.

Notes

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Argues that of the two categories of variability, continuous and intermittent (discrete), only discrete variability is inherited. Developed by Goal. botanist H. De Vries in 1901 1903. Main. provisions of M. t.: mutation occurs suddenly... Biological encyclopedic dictionary

Mutation theory- * mutation theory * mutation theory is a theory based on the recognition of the heritability of only discrete (mutational) changes in the genome of an organism. M. t. was developed by G. de Vries in 1901-1903. A number of its provisions (creation of species in... ... Genetics. Encyclopedic Dictionary

It arose as a result of the discovery of mutations of hereditary changes in the characteristics and properties of organisms. According to the mutation theory (Russian scientist S.I. Korzhinsky, 1899, Dutch H. De Vries, 1901 1903), sharp, sudden mutations are the decisive factor... Big Encyclopedic Dictionary

It arose as a result of the discovery of mutations of hereditary changes in the characteristics and properties of organisms. According to the mutation theory (Russian scientist S.I. Korzhinsky, 1899, Dutch H. De Vries, 1901 03), sharp, sudden mutations are decisive... ... Encyclopedic Dictionary

Mutation theory mutation theory. The theory, based on the recognition of the heritability of only discrete (mutational) changes in the body, was developed by H. De Vries in 1901 03; a number of provisions of M.t. (creation of species as a result of mutations without selection, etc.),… … Molecular biology and genetics. Explanatory dictionary.

mutation theory- PATHOLOGY OF EMBRYOGENESIS MUTATION THEORY. BASIC PROVISIONS OF MUTATION THEORY – 1. Mutations arise suddenly, spasmodically, without any transitions and do not form continuous series. 2. Mutations are inherited. 3. They are non-directional, i.e.... General embryology: Terminological dictionary

The theory of variability and evolution, created at the beginning of the 20th century. H. De Vries. According to M. t., of the two categories of variability, continuous and intermittent (discrete), only the latter is hereditary; to designate it, De Vries introduced the term Mutation.... ... Great Soviet Encyclopedia

The theory of the origin of species, put forward in the beginning. 20th century H. de Vries, according to which new species arise from old ones in leaps and bounds, through large hereditary changes in mutations. New dictionary of foreign words. by EdwART, 2009 … Dictionary of foreign words of the Russian language

It arose as a result of the discovery of inherited mutations. changes in the characteristics and properties of organisms. According to M.t. (X. De Vries, 1901 03), sharp, sudden mutations are a decisive factor in evolution, immediately leading to the emergence of new species; natural selection... ... Natural science. Encyclopedic Dictionary

The style of this article is non-encyclopedic or violates the norms of the Russian language. The article should be corrected according to Wikipedia's stylistic rules. The mutation theory of carcinogenesis is the doctrine according to which the cause of the occurrence of malignant tumors is ... Wikipedia

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The importance of biology for humans is enormous. Thanks to knowledge of the laws of heredity and variability, great successes have been achieved in agriculture in the creation of new highly productive breeds of domestic animals and varieties of cultivated plants. Hundreds of varieties of grains, legumes, oilseeds and other crops have been developed,

Mutation theory. Types of mutations

Mutational variability

Mutations are hereditary changes in genotypic material. They are characterized as rare, random, undirected events. Most mutations lead to various disorders of normal development, some of them are lethal, but at the same time, many mutations are the starting material for natural selection and biological evolution.

The frequency of mutations increases under the influence of certain factors - mutagens, which can change the material of heredity. Depending on their nature, mutagens are divided into physical (ionizing radiation, UV radiation, etc.), chemical (a large number of different compounds), biological (viruses, mobile genetic elements, some enzymes). The division of mutagens into endogenous and exogenous is very arbitrary. Thus, ionizing radiation, in addition to primary DNA damage, forms unstable ions (free radicals) in the cell that can secondary cause damage to genetic material. Many physical and chemical mutagens are also carcinogens, i.e. induce malignant cell growth.

The mutation rate follows the Poisson distribution, which is used in biometrics when the probability of an individual event is very small and the sample in which the event can occur is large. The probability of mutations in a single gene is quite low, but the number of genes in the body is large, and in the gene pool of the population it is huge.

In the literature you can find various mutations: by manifestation in a heterozygote (dominant, recessive), by ionizing factor (spontaneous, induced), by localization (generative, somatic), by phenotypic manifestation (biochemical, morphological, behavioral, lethal, etc.).

Mutations are classified according to the nature of the genome change. Based on this indicator, 4 groups of mutations are distinguished.

Genetic - changes in the nucleotide composition of the DNA of individual genes.

Chromosomal (aberrations) – changes in the structure of chromosomes.

Genomic – changes in the number of chromosomes.

Cytoplasmic – changes in non-nuclear genes.

Mutation theory

Mutation theory, or more correctly, the theory of mutations, is one of the foundations of genetics. It originated shortly after the first discovery of G. Mendel's laws in the works of G. De Vries (1901-1903). Even earlier, the Russian botanist S.I. came to the idea of ​​abrupt changes in hereditary properties. Korzhinsky (1899) in his work “Heterogenesis and Evolution”. It is fair to talk about the mutation theory of Korzhenevsky - De Vries, who devoted most of his life to studying the problem of mutational variability in plants.

At first, mutation theory focused entirely on the phenotypic manifestation of hereditary changes, with virtually no attention to the mechanism of their manifestation. In accordance with the definition of G. De Vries, a mutation is the phenomenon of spasmodic, intermittent changes in a hereditary trait. Until now, despite numerous attempts, there is no concise definition of mutation better than that given by G. De Vries, although it is not free from shortcomings.

The main provisions of the mutation theory of G. De Vries are as follows:

1. Mutations arise suddenly as discrete changes in characteristics.

2. New forms are stable.

3. Unlike non-hereditary changes, mutations do not form continuous series and are not grouped around any average type. They represent qualitative changes.

4. Mutations manifest themselves in different ways and can be either beneficial or harmful.

5. The probability of detecting a mutation depends on the number of individuals examined.

6. Similar mutations can occur repeatedly.

Like many geneticists of the early period, G. De Vries mistakenly believed that mutations could immediately give rise to new species, i.e. bypassing natural selection.

G. De Vries created his mutation theory based on experiments with various species of Oenothera. In fact, he did not receive mutations, but observed the result of combinative variability, since the forms with which he worked turned out to be complex heterozygotes for translocation.

The honor of rigorous proof of the occurrence of mutations belongs to V. Johansen, who studied inheritance in pure (self-pollinating) lines of beans and barley. The result he obtained concerned a quantitative characteristic—seed mass. The dimensional values ​​of such characteristics necessarily vary, being distributed around a certain average value. Mutational changes in such characteristics were discovered by V. Johannsen (1908-1913). This fact itself already poses one of the provisions of G. De Vries (point 3, mutation theory of G. De Vries).

One way or another, the hypothesis about the possibility of abrupt hereditary changes - mutations, which was discussed by many geneticists at the turn of the century (including W. Bateson), received experimental confirmation.

The largest generalization of work on the study of variability at the beginning of the 20th century. became the law of homological series in hereditary variability N.I. Vavilov, which he formulated in 1920 in a report at the III All-Russian Selection Congress in Saratov. According to this law, similar species and genus of organisms are characterized by similar series of hereditary variability. The closer the taxonomically considered organisms are, the greater the similarity is observed in the series (spectrum) of their variability. The fairness of this law N.I. Vavilov illustrated it using a huge amount of botanical material.

Law N.I. Vavilova finds confirmation in the study of the variability of animals and microorganisms, not only at the level of whole organisms, but also of individual structures. It is obvious that the law of N.I. Vavilova stands among the scientific achievements that led to modern ideas about the universality of many biological structures and functions.

Law N.I. Vavilova is of great importance for breeding practice, since it predicts the search for certain forms of cultivated plants and animals. Knowing the nature of variability of one or several closely related species, one can purposefully search for forms that are not yet known in a given organism, but have already been discovered in its taxonomic relatives.

Classification of mutations

The difficulties of defining the concept of “mutation” are best illustrated by the classification of its types.

There are several principles for this classification.

A. By the nature of the genome change:

1. Genomic mutations – changes in the number of chromosomes.

2. Chromosomal mutations, or chromosomal rearrangements, are changes in the structure of chromosomes.

3. Gene mutations - changes in genes.

B. By manifestation in a heterozygote:

1. Dominant mutations.

2. Recessive mutations.

B. By deviation from the norm or the so-called wild type:

1. Direct mutations.

2. Reversions. Sometimes they talk about reverse mutations, but it is obvious that they represent only a part of the reversions, since in reality so-called suppressor mutations are widespread.

D. Depending on the reasons causing mutations:

1. Spontaneous, occurring for no apparent reason, i.e. without any inducing influences from the experimenter.

2. Induced mutations.

Only these four methods of classifying changes in genetic material are quite strict and have universal significance. Each approach in these classification methods reflects some significant aspect of the occurrence or manifestation of mutations in any organisms: eukaryotes, prokaryotes and their viruses.

There are also more specific approaches to classifying mutations:

D. By localization in the cell:

1. Nuclear.

2. Cytoplasmic. In this case, mutations of non-nuclear genes are usually implied.

E. In relation to the possibility of inheritance:

1. Generative, occurring in germ cells.

2. Somatic, occurring in somatic cells.

Obviously, the last two methods of classifying mutations are applicable to eukaryotes, and consideration of mutations from the point of view of their occurrence in somatic or germ cells is relevant only to multicellular eukaryotes.

Very often, mutations are classified according to their phenotypic manifestation, i.e. depending on the changing characteristic. Then lethal, morphological, biochemical, behavioral, resistance or sensitivity to damaging agents mutations, etc. are considered.

In general terms, we can say that mutations are heritable changes in genetic material. Their appearance is judged by changes in signs. This primarily applies to gene mutations. Chromosomal and genomic mutations are also expressed in changes in the nature of inheritance of traits.

§ 2. Mutation theory

Discovery of intermittent, sudden, hereditary undirected changes - mutations(from lat. mutation- change) *, the distribution of which is purely random, served as an impetus for an even more rapid development of classical genetics at the beginning of the 20th century and for elucidating the role of hereditary changes in evolution.

* (Sudden hereditary changes have long been called mutations (in the 17th and 18th centuries). This term was resurrected by G. De Vries.)

In 1898, a Russian botanist S. I. Korzhinsky, and two years later, the Dutch botanist De Vries (one of those who rediscovered Mendel’s law - see Chapter IV, § 3) independently made another extremely important genetic generalization, called mutation theory.

The essence of this theory is that mutations arise suddenly and undirectedly, but once they occur, the mutation becomes stable. The same mutation can occur repeatedly.

One day, passing by a potato field (near the Dutch village of Gilversum), overgrown with the weed brought from America, night candle or evening primrose ( Oenothera Lamarckiana) from the fireweed family (which includes the well-known fireweed, or fireweed), De Vries noticed among ordinary plants specimens that differed sharply from them. The scientist collected the seeds of these exceptional plants and sowed them in his experimental garden. For 17 years, De Vries observed evening primrose (thousands of plants). At first, he discovered three mutants: one of them was dwarf, the other was giant - its leaves, flowers, fruits, seeds turned out to be large, its stems were long (Fig. 29), the third had red veins on the leaves and fruits. Over the course of 10 years, De Vries obtained many new forms from normal plants, differing in a number of characteristics. The scientist closely followed mutants(as mutation carriers are called) and their descendants for several years. Based on observations, complementing the teachings of Darwin, he came to the conclusion about the paramount importance of sharp hereditary deviations - mutations for the emergence of new species. Mutations appear in a variety of directions in representatives of any of the species. Since not all mutations allow a mutant to survive (in a certain environment), the further existence of the corresponding form is decided by Darwinian the struggle for existence through natural selection.

Soon, many descriptions of various mutations in animals and plants appeared in the scientific literature.

Without knowing the mechanism by which mutations occur, De Vries believed that all such changes arise spontaneously, spontaneously. This situation is true only for some mutations.

The inevitability of spontaneous mutations follows from the inevitability of the movement of atoms, in which sooner or later, but statistically inevitably, transitions of electrons from one orbit to another occur. As a result, individual atoms and entire molecules change even under the most constant environmental conditions. This inevitable change in any physical and chemical structure is reflected in the appearance of spontaneous mutations (DNA molecules, the custodians of hereditary information, are such a structure).

Spontaneous mutations are constantly found in nature with a certain frequency, which is relatively similar in a wide variety of species of living organisms. The frequency of occurrence of spontaneous mutations varies for individual characteristics from one mutation per 10 thousand gametes to one mutation per 10 million gametes. However, due to the large number of genes in each individual in all organisms, 10-25% of all gametes carry certain mutations. Approximately every tenth individual is a carrier of a new spontaneous mutation.

It should be noted that the majority of newly emerging mutations are usually in a recessive state, increasing only the latent, potential variability characteristic of organisms of any species. When environmental conditions change, for example, when the action of natural selection changes, this hidden hereditary variability can manifest itself, since individuals carrying recessive mutations in a heterozygous state will not be destroyed in the new conditions in the process of struggle for existence, but will remain and produce offspring. Spontaneous, spontaneous mutations appear without any outside intervention. However, there are many so-called induced mutations. Factors causing (inducing) mutations can be a wide variety of environmental influences: temperature, ultraviolet radiation, radiation (both natural and artificial), the action of various chemical compounds - mutagens. Mutagens are agents of the external environment that cause certain changes in the genotype - mutation, and the process of mutation formation 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 history, geneticists used X-rays to produce mutations in yeast. A year later, an American researcher G. Meller(later twice Nobel Prize laureate), who worked for a long time in Moscow, at the institute led by N. K. Koltsov, used the same mutagen on Drosophila.

Numerous mutations have been discovered in Drosophila, two of them, vestigial and curled, are shown in Fig. 30.

Currently, work in this area has grown into one of the sciences - radiation biology, a science that has great practical application. For example, some mutations of fungi that produce antibiotics give hundreds and even thousands of times greater yield of medicinal substances. In agriculture, mutations have produced high-yielding plants. Radiation genetics is important in the study and exploration of outer space.

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 M. E. Lobashov.

Chemical mutagens include a wide variety of substances (alkylating compounds, hydrogen peroxide, aldehydes and ketones, nitrous 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 (from the Latin herba - grass), drugs, alcohol, nicotine, some medicinal substances and many others.

In recent years, work has begun in our country to use chemical mutagens to create new breeds of animals. Interesting results have been achieved in changing the coat color of rabbits and increasing the length of wool in sheep. It is important that these achievements were obtained at dosages of mutagens that do not cause death in experimental animals. The strongest chemical mutagens (nitrosoalkylureas, 1,4-bisdiazoacetylbutane) are widely used.

One of the main tasks of selection agricultural plants is the creation of varieties resistant to fungal and viral diseases. Chemical mutagens are an effective means of obtaining plant forms that are resistant to a wide variety of diseases. Forms resistant to powdery mildew and increased resistance to various types of rust have been obtained from cereals (spring and winter wheat, barley, oats). It is important that in individual mutants an increase in the amount of protein does not correlate with a deterioration in its quality and it is possible to obtain forms with an increased content of protein and essential amino acids in it (lysine, methionine, threonine).

Among mutants induced by chemical mutagens, forms with a complex of positive characteristics are of great interest. There are frequent cases of obtaining such forms from wheat, peas, tomatoes, potatoes and other crops. Mutations are the material for both natural, and for artificial selection(selection).

In 1920, still young at that time, but one of the greatest geneticists of the 20th century, Nikolai Ivanovich Vavilov, established that there is parallelism of variability among the most diverse systematic units of living beings. This provision is called the rule homological(from lat. homologis- agreement, common origin) of series, which to a certain extent makes it possible to predict what mutations may occur in related (and sometimes distant) forms. This rule is that between different systematic groups (species, genera, classes and even types) there are repeating series of forms that are similar in their morphological and physiological properties. This similarity is due to the presence of common genes and their similar mutations.

Thus, among the varieties of wheat and rye there are similar forms, winter and spring, with an awned, short-awned or awnless ear; Both have drooping, smooth-spiked, red-, white- and black-spiked races, races with brittle and non-brittle spikes and other characteristics. A similar parallelism between organisms belonging to different species, genera, families, and even different classes is observed in animals. An example would be gigantism, dwarfism or lack of pigmentation- albinism in mammals, birds, as well as in other animals and plants.

Having discovered a series of forms A, B, C, D, D, E in one biological species and having established forms A 1, B 1, D 1, E 1 in another related species, we can assume that there are still undiscovered forms B 1 and G 1.

In humans, the mutation rate under natural conditions is 1:1,000,000, but if we take into account the huge number of genes, then at least 10% of gametes, both male and female, carry some kind of newly emerging mutation.

Mutation theory or mutation theory- a branch of genetics that lays the foundations of genetic variability and evolution.

Emergence

Mutation theory is one of the foundations of genetics. It originated shortly after Mendel's laws at the beginning of the 20th century. It can be considered that it almost simultaneously arose in the minds of the Dutchman Hugo de Vries (1903) and the domestic botanist S.I. Korzhinsky (1899). However, the priority in primacy and in greater coincidence of the original provisions belongs to the Russian scientist. The recognition of the main evolutionary significance of discrete variability and the denial of the role of natural selection in the theories of Korzhinsky and De Vries was associated with the intractability at that time of the contradiction in the evolutionary teachings of Charles Darwin between the important role of small deviations and their “absorption” during crossings (see the nightmare of Jenkin and History of evolutionary doctrine#Crisis of Darwinism).

Basic provisions

The main provisions of the Korzhinsky-De Vries mutation theory can be reduced to the following points:

1. Mutations are sudden, like discrete changes in traits.
2. New forms are stable.
3. Unlike non-hereditary changes, mutations do not form continuous series and are not grouped around any average type. They represent qualitative leaps in change.
4. Mutations manifest themselves in different ways and can be either beneficial or harmful.
5. The probability of detecting mutations depends on the number of individuals studied.
6. Similar mutations can occur repeatedly.

Research by H. De Vries was carried out on various species of Oslinnik ( Oenothera), which during the experiment did not produce mutations, but showed complex combinative variability, since these forms were complex heterozygotes for translocations.

Strict proof of the occurrence of mutations belongs to V. Johansen based on experiments on self-pollinating lines of beans and barley - seed masses were studied, mutational changes in this trait were discovered by V. Johansen (1908-1913). It is noteworthy that, even having a mutational nature, the mass of seeds was distributed relative to certain average values, thereby casting doubt on the third point of the mutation theory.

Mutation theory or mutation theory- a branch of genetics that lays the foundations of genetic variability and evolution.

Emergence

Mutation theory is one of the foundations of genetics. It originated shortly after Mendel's laws at the beginning of the 20th century. It can be considered that it almost simultaneously arose in the minds of the Dutchman Hugo de Vries (1903) and the domestic botanist S.I. Korzhinsky (1899). However, the priority in primacy and in greater coincidence of the original provisions belongs to the Russian scientist. The recognition of the main evolutionary significance of discrete variability and the denial of the role of natural selection in the theories of Korzhinsky and De Vries was associated with the intractability at that time of the contradiction in the evolutionary teachings of Charles Darwin between the important role of small deviations and their “absorption” during crossings (see the nightmare of Jenkin and History of evolutionary doctrine#Crisis of Darwinism).

Basic provisions

The main provisions of the Korzhinsky-De Vries mutation theory can be reduced to the following points:

1. Mutations are sudden, like discrete changes in traits
2. New forms are stable
3. Unlike non-hereditary changes, mutations do not form continuous series and are not grouped around any average type. They represent qualitative leaps in change
4. Mutations manifest themselves in different ways and can be either beneficial or harmful.
5. The probability of detecting mutations depends on the number of individuals studied
6. Similar mutations can occur repeatedly

Research by H. De Vries was carried out on various species of Oenothera, which during the experiment did not produce mutations, but showed complex combinative variability, since these forms were complex heterozygotes for translocations.

Strict proof of the occurrence of mutations belongs to V. Johannsen based on experiments on self-pollinating lines of beans and barley - seed masses were studied, mutational changes in this trait were discovered by V. Johannsen (1908-1913). It is noteworthy that, even having a mutational nature, the mass of seeds was distributed relative to certain average values, thereby casting doubt on the third point of the mutation theory.

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Excerpt characterizing Mutation Theory