In this case, the resulting specific modified change in the trait is not inherited, but the range of such variability, or the reaction rate, is genetically determined and inherited. Modifications persist only throughout the life of a given organism.

Both quantitative and qualitative characteristics are subject to modification variability. The appearance of modifications is due to the fact that such important environmental factors as light, heat, moisture, the chemical composition and structure of the soil, air, affect the activity of enzymes and, to a certain extent, change the course of biochemical reactions occurring in a developing organism. This, in particular, explains the appearance of different colors of flowers in primrose and wool in Himalayan rabbits, as mentioned above.

Examples of modification variability in humans are increased skin pigmentation (sunburn) under the influence of ultraviolet rays, powerful development of the musculoskeletal system as a result of physical exertion, etc. Modification variability should also include the phenomenon of physiological homeostasis - the ability of organisms to withstand fluctuating environmental conditions by adaptive response. So, when a person is at different heights above sea level, an unequal number of erythrocytes is produced: in 1 mm j of blood in people living in areas at sea level, there are two times less of them than in people living high in the mountains.

The number of red blood cells increases in proportion to the rise above sea level. This phenomenon can be easily explained if we remember that the main function of red blood cells is to carry oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. An increase in altitude is accompanied by a decrease in the concentration of oxygen in the atmosphere, which leads to a lack of oxygen in the tissues. Therefore, the urgent need for oxygen forces humans and animals to adaptively respond by changing the number of red blood cells at different altitudes.

This reaction is reversible: moving to places located at sea level leads to a decrease in the number of red blood cells in the blood.

Statistical analysis of modification variability. Such conditional environments as humidity, temperature, illumination, physical properties of the soil and its fertility, the depth of planting seeds, the interaction and competition of plants with other cohabitants, are never identical even in the same field. Therefore, the length of ears of wheat in one field can vary from 6 to 14 cm, and the sizes of leaves of one tree sometimes vary in even wider limits, although their genotype is the same. If the leaves or ears are arranged in the order of increasing or decreasing their length, it turns out variation series of variability of this feature, consisting of separate option, that is, the number of leaves of a tree or spikelets in an ear of wheat that have the same indicators.

Calculations show that the frequency of occurrence of individual variants in the variation series is not the same. Most often, the average value of the trait is found, and towards both ends of the variation series, the frequency of occurrence naturally decreases. Let us consider this using the example of the variability of the number of spikelets in an ear of wheat. Let's take randomly (without choosing) 100 ears of the same sort and count the number of ears in each of them. The resulting numbers (options) are arranged in the increasing order of the feature and calculate how many times each option v occurs in each row R, then we group them, that is, we compose a variation series:

The distribution of the variant in this series can be expressed graphically on the graph (Fig. 3.12). To do this, the values ​​of variant v are plotted on the abscissa axis in the order of their increase, on the ordinate axis - the frequency of occurrence R each option.

The graphic expression of the variability of a trait, reflecting both the range of variations and the frequency of occurrence of individual variants, is called variation curve. It was found that modification variability in plants, animals and humans has common features.

Rice. 3.12... Variation curve of the number of spikelets in an ear of wheat.

The curve on the graph is usually symmetrical, especially when a large number of individuals are being studied. This means that variations, both large and small, differing from the arithmetic mean by the same amount, occur equally often. It follows that the minimum and maximum values ​​should be encountered very rarely, but with the same frequency.

The meaning of the modifications. Modification variability in natural conditions is of an adaptive nature and in this sense is of great importance in evolution. Adaptive modifications conditioned by the reaction norm enable the organism to survive and leave offspring in the changed environmental conditions.

Knowledge of the patterns of modification variability is also of great practical importance, since it allows one to foresee and plan in advance the maximum use of the capabilities of each plant variety and animal breed. In particular, the creation of known optimal conditions for the realization of the genotype ensures their high productivity.

This approach applies equally to humans. Each child has certain abilities, sometimes even in several areas. The task of psychologists and teachers is to find this area as early as possible and to ensure the maximum development of the child in this direction (along with general education), i.e., within the limits of the reaction norm, to achieve the maximum level of realization of his genotype.

Abstract on the topic: Forms of variability

Variability is the emergence of individual differences. On the basis of the variability of organisms, a genetic diversity of forms appears, which, as a result of the action of natural selection, are transformed into new subspecies and species. Distinguish between modification, or phenotypic, and mutational, or genotypic variability.

Table 1.

(T. L. Bogdanova. Biology. Tasks and exercises. A guide for applicants to universities. M., 1991).

Forms of variability		Reasons for the appearance	Meaning	Examples of
Non-hereditary modification (phenotypic)		Changes in environmental conditions, as a result of which the organism changes within the normal range of the reaction given by the genotype	Adaptation - adaptation to given environmental conditions, survival, preservation of offspring	White cabbage in hot climates does not form a head of cabbage. Horse and cow breeds brought into the mountains become stunted
Hereditary (genotypic)	Mutational	The influence of external and internal mutagenic factors, resulting in a change in genes and chromosomes	Material for natural and artificial selection, since mutations can be beneficial, harmful and indifferent, dominant and recessive	The appearance of polyploid forms in a plant population or in some animals (insects, fish) leads to their reproductive isolation and the formation of new species, genera - microevolution
	Combinative	Occurs spontaneously within the population during crossing, when new combinations of genes appear in the offspring	Distribution of new hereditary changes in the population, which serve as material for selection	The appearance of pink flowers when crossing white-flowered and red-flowered primroses. When crossing white and gray rabbits, black offspring may appear
	Relative (correlative)	It arises as a result of the properties of genes to influence the formation of not one, but two or more signs	The constancy of interrelated signs, the integrity of the organism as a system	Long-legged animals have a long neck. In table varieties of beets, the color of the root crop, petioles and leaf veins changes consistently

Modification variability

Modification variability does not cause changes in the genotype, it is associated with the reaction of a given, one and the same genotype to a change in the external environment: under optimal conditions, the maximum of possibilities inherent in a given genotype is revealed. Thus, the productivity of outbred animals in conditions of improved housing and care increases (milk yield, fattening of meat). In this case, all individuals with the same genotype respond to external conditions in the same way (Charles Darwin called this type of variability a certain variability). However, another sign - the fat content of milk - is weakly susceptible to changes in environmental conditions, and the color of the animal is an even more stable sign. Modification variability usually fluctuates within certain limits. The degree of variation of a trait in an organism, that is, the limits of modification variability, is called the reaction norm. A wide reaction rate is characteristic of such traits as milk yield, leaf size, color in some butterflies; a narrow reaction rate - fat content of milk, egg production in chickens, intensity of color of corolla in flowers, and more. The phenotype is formed as a result of interactions between genotype and environmental factors. Phenotypic traits are not transmitted from parents to offspring, only the reaction rate is inherited, that is, the nature of the response to changes in environmental conditions. In heterozygous organisms, changing environmental conditions can cause various manifestations of this trait.

Modification properties:

1) non-heritability;

2) the group nature of the changes;

3) correlating changes to the action of a certain environmental factor;

4) the determination of the limits of variability by the genotype.

Genotypic variability

Genotypic variability is subdivided into mutational and combinative. Mutations are called abrupt and stable changes in units of heredity - genes, entailing changes in hereditary traits. The term "mutation" was first coined by de Vries. Mutations necessarily cause changes in the genotype, which are inherited by the offspring and are not associated with crossing and recombination of genes.

Classification of mutations

Mutations can be grouped into groups - classified by the nature of their manifestation, by place, or by the level of their occurrence.

Mutations by the nature of manifestation are dominant and recessive. Mutations often reduce vitality or fertility. Mutations that sharply reduce vitality, partially or completely stop development, are called semi-lethal, and those incompatible with life are called lethal.

Mutations are classified according to their place of origin. A mutation that has arisen in the germ cells does not affect the characteristics of a given organism, but manifests itself only in the next generation. Such mutations are called generative. If genes change in somatic cells, such mutations appear in this organism and are not transmitted to offspring during sexual reproduction. But with asexual reproduction, if an organism develops from a cell or group of cells that have a changed - mutated - gene, mutations can be passed on to offspring. Such mutations are called somatic.

Mutations are classified according to their level of occurrence. There are chromosomal and gene mutations. Mutations also include a change in the karyotype (change in the number of chromosomes). Polyploidy - an increase in the number of chromosomes, a multiple of the haploid set. In accordance with this, in plants, triploids (Zn), tetraploids (4n), etc. are distinguished. More than 500 polyploids are known in plant growing (sugar beet, grapes, buckwheat, mint, radish, onion, etc.). All of them are distinguished by a large vegetative mass and are of great economic value.

A wide variety of polyploids is observed in floriculture: if one original form in a haploid set had 9 chromosomes, then cultivated plants of this species can have 18, 36, 54 and up to 198 chromosomes. Polyploids are obtained as a result of exposure of plants to temperature, ionizing radiation, chemicals (colchicine), which destroy the spindle of cell division. In such plants, the gametes are diploid, and when they merge with the haploid sex cells of the partner, a triploid set of chromosomes (2n + n = Zn) appears in the zygote. Such triploids do not form seeds, they are sterile, but high-yielding. Even polyploids form seeds. Heteroploidy is a change in the number of chromosomes that is not a multiple of the haploid set. In this case, the set of chromosomes in a cell can be increased by one, two, three chromosomes (2n + 1; 2n + 2; 2n + 3) or decreased by one chromosome (2n-1). For example, a person with Down's syndrome has one extra chromosome on the 21st pair and the karyotype of such a person is 47 chromosomes. In people with Shereshevsky-Turner syndrome (2n-1), one X chromosome is missing and 45 chromosomes remain in the karyotype. These and other similar deviations of numerical relationships in a person's karyotype are accompanied by a health disorder, mental and physical disorders, a decrease in vitality, etc.

Chromosomal mutations associated with a change in the structure of chromosomes. There are the following types of chromosome rearrangements: the detachment of various parts of the chromosome, the doubling of individual fragments, the rotation of a part of the chromosome by 180 °, or the attachment of a separate part of the chromosome to another chromosome. Such a change entails a violation of the function of genes in the chromosome and the hereditary properties of the organism, and sometimes its death.

Gene mutations affect the structure of the gene itself and entail a change in the properties of the organism (hemophilia, color blindness, albinism, color of the corolla of flowers, etc.). Gene mutations occur in both somatic and germ cells. They can be dominant and recessive. The former are manifested both in homozygotes and in heterozygotes, the latter - only in homozygotes. In plants, the somatic gene mutations that have arisen are preserved during vegetative reproduction. Mutations in germ cells are inherited during seed reproduction of plants and during sexual reproduction of animals. Some mutations have a positive effect on the body, others are indifferent, and still others are harmful, causing either the death of the body or weakening its vitality (for example, sickle cell anemia, hemophilia in humans).

When breeding new varieties of plants and strains of microorganisms, induced mutations are used, artificially caused by certain mutagenic factors (X-rays or ultraviolet rays, chemicals). Then, the obtained mutants are selected, keeping the most productive ones. In our country, these methods have obtained many economically promising varieties of plants: non-sticking wheat with large ears, resistant to diseases; high-yielding tomatoes; cotton plant with large bolls, etc.

Properties of mutations

1. Mutations occur suddenly, in leaps and bounds.

2. Mutations are hereditary, that is, they are steadily passed from generation to generation.

3. Undirected mutations - any locus can mutate, causing changes in both minor and vital signs.

4. The same mutations can occur repeatedly.

5. By their manifestation, mutations can be useful and harmful, dominant and recessive.

The ability to mutate is one of the properties of a gene. Each individual mutation is caused by a cause, but in most cases, these causes are unknown. Mutations are associated with changes in the external environment. This is convincingly proven by the fact that through exposure to external factors, it is possible to dramatically increase their number.

Combinative variability

Combinative hereditary variability arises as a result of the exchange of homologous regions of homologous chromosomes during meiosis, as well as as a consequence of the independent divergence of chromosomes during meiosis and their random combination during crossing. Variability can be caused not only by mutations, but also by combinations of individual genes and chromosomes, a new combination of which, during reproduction, leads to a change in certain characteristics and properties of the organism. This type of variability is called combinative hereditary variability. New combinations of genes arise:

1) with crossing over, during the prophase of the first meiotic division;

2) during the independent divergence of homologous chromosomes in the anaphase of the first meiotic division;

3) during the independent divergence of daughter chromosomes in the anaphase of the second meiotic division

4) when different germ cells merge.

The combination of recombined genes in a zygote can lead to a combination of traits of different breeds and varieties.

In breeding, the law of homologous series of hereditary variation, formulated by the Soviet scientist N.I. Vavilov, is of great importance. It reads:

Within different species and genera, genetically close (i.e., having a single origin), similar series of hereditary variability are observed. Such a character of variability was revealed in many cereals (rice, wheat, oats, millet, etc.), in which the color and consistency of grain, cold resistance, and other qualities vary similarly. Knowing the nature of hereditary changes in some varieties, one can predict similar changes in related species and, acting on them with mutagens, cause similar beneficial changes in them, which greatly facilitates the production of economically valuable forms. Many examples of homologous variation in humans are also known; for example, albinism (a defect in the synthesis of a dye by cells) is found in Europeans, Negroes and Indians; among mammals - in rodents, carnivores, primates; small dark-skinned people - pygmies are found in the tropical forests of equatorial Africa, in the Philippine Islands and in the jungle of the Malacca Peninsula; some hereditary defects and deformities inherent in humans are also noted in animals. Such animals are used as a model to study similar defects in humans. For example, cataracts of the eye occur in a mouse, rat, dog, horse; hemophilia - in mice and cats, diabetes - in rats; congenital deafness - in a guinea pig, mouse, dog; hare lip - in mice, dogs, pigs, etc. These hereditary defects are a convincing confirmation of the law of homologous series of hereditary variability of NI Vavilov.

Table 2.

Comparative characteristics of the forms of variability

(T. L. Bogdanova. Biology. Tasks and exercises. A guide for applicants to universities. M., 1991)

Characteristic	Modification variability	Mutational variability
Change object	Phenotype within the normal reaction range
Selection factor	Changing environmental conditions Wednesday	Changing environmental conditions
Inheritance with signs	Not inherited	Are inherited
Exposure to chromosome changes	Not exposed	Undergo a chromosomal mutation
Susceptibility to changes in DNA molecules	Not exposed	Exposed in case gene mutation
Meaning for an individual	Increases or lowers vitality. productivity, adaptation	Useful changes lead to victory in the struggle for existence, harmful - to death
Value for the view	Promotes survival	Leads to the formation of new populations, species, etc. as a result of divergence
Role in evolution	Adaptation organisms to environmental conditions	Material for natural selection
Variation form	Certain (group)	Indefinite (individual), combinative
Subordination to regularity	Statistical regularity variation series	Homologous law ranks of hereditary variation

Variability(biological), a variety of traits and properties in individuals and groups of individuals of any degree of relationship. Variability is inherent in all living organisms, therefore, there are no individuals in nature that are identical in all signs and properties. The term "Variability" is also used to denote the ability of living organisms to respond with morphophysiological changes to external influences and to characterize the transformations of forms of living organisms in the process of their evolution.

Variability can be classified according to the causes, nature and nature of the changes, as well as the goals and methods of research.

Distinguish variability: hereditary (genotypic) and non-hereditary (paratypical); individual and group; intermittent (discrete) and continuous; qualitative and quantitative; independent variability of different characters and correlative (relational); directed (determined, according to Charles Darwin) and undirected (undefined, according to Charles Darwin); adaptive (adaptive) and non-adaptive. When solving general problems of biology and especially evolution, the most important subdivision of variability, on the one hand, into hereditary and non-hereditary, and on the other, into individual and group. All categories of variability can occur in hereditary and non-hereditary, group and individual variability.

Hereditary variability is due to the emergence of different types of mutations and their combinations in subsequent crosses. In each rather long-term (in a number of generations) existing set of individuals, various mutations arise spontaneously and non-directionally, which are then combined, more or less randomly, with different hereditary properties already present in the aggregate. The variability caused by the occurrence of mutations is called mutational, and the variability caused by further recombination of genes as a result of crossing is called combinational. All the variety of individual differences is based on hereditary variability, which include:

a) both sharp qualitative differences, not related to each other by transitional forms, and purely quantitative differences that form continuous series, in which close members of the series can differ from each other as little as desired;

b) both changes in individual traits and properties (independent variability) and interrelated changes in a number of traits (correlative variability);

c) both changes that have an adaptive value (adaptive variability) and changes that are "indifferent" or even reduce the viability of their carriers (non-adaptive variability).

All these types of hereditary changes make up the material of the evolutionary process. In the individual development of an organism, the manifestation of hereditary traits and properties is always determined not only by the main genes responsible for these traits and properties, but also by their interaction with many other genes that make up the genotype of an individual, as well as by the conditions of the external environment in which the organism develops.

The concept of non-hereditary variability includes those changes in traits and properties that in individuals or certain groups of individuals are caused by the influence of external factors (nutrition, temperature, light, humidity, etc.). Such non-hereditary traits (modifications) in their specific manifestation in each individual are not inherited, they develop in individuals of subsequent generations only in the presence of the conditions in which they arose. This variability is also called modification. For example, the color of many insects darkens at low temperatures, and brightens at high temperatures; however, their offspring will be colored regardless of the parental coloration according to the temperature at which they developed themselves. There is another form of non-hereditary variability - the so-called long-term modifications, which are often found in unicellular organisms, but are occasionally observed in multicellular organisms. They arise under the influence of external influences (for example, temperature or chemical) and are expressed in qualitative or quantitative deviations from the original form, usually gradually fading out during subsequent reproduction. They are based, apparently, on changes in relatively stable cytoplasmic structures.

There is a close relationship between non-hereditary and hereditary variability. There are no non-hereditary (literally) signs and properties, since non-hereditary changes are a reflection of the hereditary ability of organisms to respond to certain changes in signs and properties to the effects of environmental factors. In this case, the limits of non-hereditary changes are determined by the norm of the genotype's reaction to environmental conditions.

Hereditary and non-hereditary variability is studied both within individual populations of living organisms, when the differences in the characteristics of individual individuals are investigated (individual variability), and when different populations of individuals are compared with each other (group variability); individual variability also underlies any intergroup differences. Even within closely related groups, there are no absolutely identical individuals that would not differ in the severity of any hereditary or non-hereditary traits and properties. Due to the complexity of the organization of living systems, even in genotypically identical (for example, identical twins) and individuals developing in practically identical conditions, at least insignificant morphophysiological differences associated with inevitable fluctuations of environmental conditions and processes of individual development can always be found. Group variability includes differences between populations of any rank - from differences between small groups of individuals within a population to differences between the kingdoms of wildlife (animals - plants).

In essence, the entire taxonomy of organisms is based on a comparative analysis of group variability. For the study of the triggering mechanisms of the evolutionary process, various forms of intraspecific group variability are of particular importance. Most species fall into subspecies or geographic races. In the case of complete isolation of geographic forms, they can differ sharply in one or several characteristics. Populations inhabiting vast territories and not separated by sharp isolating barriers can (due to mixing and crossing) gradually pass into each other, forming quantitative gradients for one or another trait (clinal variability). Geographic, including clinal, variability in natural conditions is the result of the action of isolation, natural selection, and other factors of evolution, leading to the division of the original group of individuals in the course of the historical formation of a species into two or more groups differing in the numerical ratios of genotypes.

In some cases, differences between groups of individuals within a species are not associated with differences in their genotypic composition, but are determined by modification variability (different reactions of similar genotypes to different external conditions). The so-called seasonal variability is due to the influence on the development of the corresponding generations of different weather conditions (for example, in some insects and herbaceous plants, giving two generations a year, spring and autumn populations differ in a number of characteristics). Sometimes seasonal forms can be the result of selection of different genotypes (for example, early and late flowering forms of grasses in hay meadows: individuals blooming in summer during haymaking were eliminated for many generations). Ecological variability is of great interest - the differences between groups of individuals of the same species growing or living in different places (hills and lowlands, wetlands and dry areas, etc.). Such forms are often called ecotypes. The emergence of ecotypes can also be the result of both modification changes and the selection of genotypes that are better adapted to local conditions.

Various forms of intrapopulation polymorphism are caused by hereditary variability. In some populations, there is a coexistence of two or more clearly distinguishable forms (for example, in the two-spotted ladybug, almost all populations have a black form with red spots and a red form with black spots). This phenomenon can be based on different evolutionary mechanisms: unequal adaptability of coexisting forms to the conditions of different seasons of the year, increased viability of heterozygotes, in the offspring of which both homozygous forms are constantly segregated or other, still insufficiently studied mechanisms.

Thus, both group and individual variability include changes of both hereditary and non-hereditary nature.

Independent variability of traits is opposed by correlative variability - an interconnected change in various traits and properties: the relationship between the growth and weight of individuals (positive correlation) or the rate of cell division and the size of cells (negative correlation). Correlations can be due to purely genetic reasons (pleiotropy) or interdependencies of the processes of formation of certain traits and properties in the individual development of individuals (ontogenetic correlations), as well as similar reactions of different traits and properties to the same external influences (physiological correlations). Finally, correlations can reflect the history of the origin of populations from a mixture of two or more forms, each of which brings not individual traits, but complexes of interrelated traits and properties (historical correlations). The study of correlative variability is important in paleontology (for example, in the reconstruction of extinct forms from individual fossil remains), in anthropology (for example, in the restoration of facial features based on the study of the skull), in breeding and medicine.

The main methods for studying variability are comparative-descriptive and biometric. The combination of these methods makes it possible to study both paratypic and genotypic components of general phenotypic variability. Thus, the first can be studied by comparing genotypically identical clones and pure lines developing under different conditions. It is more difficult to distinguish purely genotypic variability from the general phenotypic one. This can be done based on biometric analysis. In medical genetics, for the same purposes, the determination of the percentage of concordance (coincidence) of certain signs in identical and fraternal twins is used.

Heredity and variability of living organisms are sometimes opposed as "conservative" and "progressive" principles. In reality, however, they are closely related. The lack of complete stability of the genotype determines mutational and (in the course of further crosses and splits) combinational variability, that is, in general, genotypic variability. Paratypical (non-hereditary) variability is the result of only the relative stability of the genotype when it determines the rate of reaction in ontogenesis during the development of traits and properties of individuals. This implies the possibility of experimental influences on both hereditary and non-hereditary variability. The first can be enhanced by the influence of mutagenic factors (radiation, temperature, chemicals). The range and direction of combination variability can be controlled by artificial selection. Non-hereditary variability can be influenced by changing the environmental conditions (nutrition, light, humidity, etc.) in which the body develops.

A clear understanding of the categories and forms of variability is necessary when constructing evolutionary schemes and theories, since the phenomena of heredity and variability underlie the evolutionary process, as well as in the practical selection of plants and animals, in the study of a number of problems in medical geography and population anthropology.

What is modification variability? Modification (phenotypic) variability of changes in the body associated with a change in the phenotype due to the influence of the environment and are, in most cases, adaptive in nature. In this case, the genotype does not change. In general, the modern concept of "adaptive modifications" corresponds to the concept of "certain variability", which was introduced into science by Charles Darwin.

Conditional classification of modification variability According to the changing characteristics of the organism: morphological changes; physiological and biochemical adaptation homeostasis (increase in the level of erythrocytes in the mountains, etc.); In terms of the range of the reaction rate: narrow (more typical for qualitative signs); wide (more typical for quantitative signs); By meaning: modifications (useful for the body are manifested as an adaptive response to environmental conditions); morphoses (non-hereditary changes in the phenotype under the influence of extreme environmental factors or modifications that arise as an expression of newly emerging mutations that do not have an adaptive nature); phenocopies (various non-hereditary changes that copy the manifestation of various mutations) a variety of morphoses; By duration: there is only an individual or a group of individuals that have been influenced by the environment (not inherited); long-term modifications persist for two to three generations.

Environment as a Cause of Modifications Modification variability is not the result of changes in the genotype, but of its response to environmental conditions. With modification variability, the hereditary material does not change, the manifestation of genes changes. Under the influence of certain environmental conditions on the body, the course of enzymatic reactions (enzyme activity) changes and specialized enzymes can be synthesized, some of which (MAP kinase, etc.) are responsible for the regulation of gene transcription, depending on environmental changes. Thus, environmental factors are able to regulate gene expression, that is, the intensity of their production of specific proteins, the functions of which correspond to specific environmental factors. For example, four genes are responsible for the production of melanin, which are located on different chromosomes. The largest number of dominant alleles of these genes 8 are found in people of the Negroid race. When exposed to a specific environment, for example, intense exposure to ultraviolet rays, destruction of epidermal cells occurs, which leads to the release of endothelin-1 and eicosanoids. They cause the activation of the tyrosinase enzyme and its biosynthesis. Tyrosinase, in turn, catalyzes the oxidation of the amino acid tyrosine. Further formation of melanin takes place without the participation of enzymes, however, a larger amount of the enzyme causes more intense pigmentation.

Reaction rate. The limit of manifestation of the organism's modification variability with a constant genotype is the norm of the reaction. The rate of reaction is determined by the genotype and differs in different individuals of a given species. In fact, the reaction norm is the spectrum of possible levels of gene expression, from which the expression level is selected that is most suitable for the given environmental conditions. The rate of reaction has a limit for each species, for example, increased feeding will lead to an increase in the weight of the animal, however, it will be within the range of the reaction rate characteristic of a given species or breed. The reaction rate is genetically determined and inherited. For different changes, there are different limits of the reaction rate. For example, the milk yield, the productivity of cereals (quantitative changes), the intensity of the color of animals, etc., vary greatly (qualitative changes). In accordance with this, the reaction rate can be wide (quantitative changes in the size of the leaves of many plants, the size of the body of many insects, depending on the feeding conditions of their larvae) and narrow (qualitative changes in coloration in pupae and adults of some butterflies). Nevertheless, some quantitative traits are characterized by a narrow reaction rate (milk fat content, the number of toes in guinea pigs), and some qualitative traits are wide (for example, seasonal color changes in many species of animals in northern latitudes).

The characteristic of modification variability, the reversibility of the change disappears when the specific environmental conditions change, which provoked their group character, changes in the phenotype are not inherited, the norm of the genotype reaction is inherited, the statistical regularity of the variation series affects the phenotype without affecting the genotype itself.

Variational series. A ranked display of the manifestation of modification variability is a variation series of modification variability of an organism's property, which consists of individual properties of modifications, arranged in order of increasing or decreasing the quantitative expression of the property (leaf size, change in the intensity of wool color, etc.). A single indicator of the ratio of two factors in a variation series (for example, the length of the coat and the intensity of its pigmentation) is called a variation. For example, wheat growing in one field can differ greatly in the number of ears and spikelets due to different indicators of the soil and moisture in the field.

Variation curve. Graphical display of the manifestation of modification variability The variation curve displays both the range of variation of the property and the frequency of individual variants. The curve shows that the most common are the average variants of the manifestation of the trait (Quetelet's law). The reason for this, apparently, is the effect of environmental factors on the course of ontogenesis. Some factors suppress gene expression, while others, on the contrary, increase it. Almost always, these factors, simultaneously acting on ontogenesis, neutralize each other, that is, neither a decrease nor an increase in the value of a trait is observed. This is the reason why individuals with extreme expressions of the trait are found in significantly smaller numbers than individuals with an average size. For example, the average height of a man of 175 cm is the most common in European populations. When constructing a variation curve, you can calculate the value of the standard deviation and, on the basis of this, build a graph of the standard deviation from the median for the most common value of the feature.

Darwinism. In 1859, Charles Darwin published his evolutionary work, The Origin of Species by Natural Selection, or the Conservation of Favorable Races in the Struggle for Life. In it, Darwin showed the gradual development of organisms as a result of natural selection. Natural selection consists of such a mechanism: first, an individual appears with new, completely random, properties (formed as a result of mutations), then it turns out or is not able to leave offspring, depending on these properties, finally, if the outcome of the previous stage turns out to be positive, then it leaves offspring and her descendants inherit the newly acquired properties

New properties of individuals. New properties of an individual are formed as a result of hereditary and modification variability. And if hereditary variability is characterized by a change in the genotype and these changes are inherited, then with modification variability, the ability of the genotype of organisms is inherited to change the phenotype when exposed to the environment. Under the constant influence of the same environmental conditions on the genotype, mutations can be selected, whose effect is similar to the manifestation of modifications, and, thus, modification variability turns into hereditary variability (genetic assimilation of modifications). An example would be the constant high percentage of melanin pigment in the skin of the Negroid and Mongoloid races compared to the Caucasian. Darwin called the modification variability specific (group). A certain variability is manifested in all normal individuals of the species that have undergone a certain influence. A certain variability expands the limits of existence and reproduction of the organism.

Natural selection and modification variability Modification variability is closely related to natural selection. Natural selection has four directions, three of which are directly aimed at the survival of organisms with different forms of non-hereditary variability. It is stabilizing, propelling, and disruptive selection. Stabilizing selection is characterized by the neutralization of mutations and the formation of a reserve of these mutations, which determines the development of the genotype with a constant phenotype. As a result, organisms with an average rate of reaction dominate under constant conditions of existence. For example, generative plants retain the shape and size of a flower that matches the shape and size of the insect that pollinates the plant. Disruptive selection is characterized by the opening of reserves with neutralized mutations and the subsequent selection of these mutations to form new genotypes and phenotypes that fit the environment. As a result, organisms with an extreme reaction rate survive. For example, insects with large wings are more resistant to wind gusts, while insects of the same species with weak wings are blown away. Driving selection is characterized by the same mechanism as disruptive selection, but it is aimed at the formation of a new average reaction rate. For example, insects develop resistance to chemicals.

Epigenetic theory of evolution According to the main provisions of the epigenetic theory of evolution, published in 1987, the substrate for evolution is a holistic phenotype, that is, morphoses in the development of an organism are determined by the impact of environmental conditions on its ontogenesis (epigenetic system). At the same time, a stable developmental trajectory is formed, based on morphoses (credo), a stable epigenetic system is formed that is adaptive to morphoses. This developmental system is based on the genetic assimilation of organisms (gene modification of copying), which is in accordance with any modification of a certain mutation. That is, this means that a change in the activity of a particular gene can be caused by both a change in the environment and a certain mutation. When a new environment acts on an organism, mutations are selected that adapt the organism to new conditions, therefore the organism, first adapting to the environment with the help of modifications, then becomes adapted to it and genetically (motor selection) a new genotype arises, on the basis of which a new phenotype arises ... For example, with congenital underdevelopment of the motor apparatus of animals, a restructuring of the supporting and motor organs occurs in such a way that the underdevelopment turns out to be adaptive. Further, this trait is fixed by hereditarily stabilizing selection. Subsequently, a new mechanism of behavior appears, aimed at adaptation to adaptation. Thus, in the epigenetic theory of evolution, postembryonic morphosis is considered on the basis of special environmental conditions as a motor lever of evolution. Thus, natural selection in the epigenetic theory of evolution consists of the following stages:

Stages of natural selection: an extreme environmental factor leads to morphoses, and morphoses to destabilization of ontogenesis, destabilization of ontogenesis leads to the manifestation of a non-standard (alternative, abnormal) phenotype, which most closely corresponds to the prevailing morphoses, if the alternative phenotype is successfully matched, there is a fixed gene copying of modifications, which leads to stabilization of ontogeny determines the direction of natural selection, a new reaction norm is established further, in the course of consolidating new properties by genocopying modifications, new alternative paths of development are formed, which are manifested during the next destabilization of ontogenesis.

Forms of modification variability. In most cases, modification variability contributes to the positive adaptation of organisms to environmental conditions, the response of the genotype to the environment improves, and a restructuring of the phenotype occurs (for example, the number of erythrocytes in a person climbing the mountains increases). However, sometimes, under the influence of unfavorable environmental factors, for example, the influence of teratogenic factors on pregnant women, phenotype changes occur, similar to mutations (not hereditary changes, similar to hereditary) phenocopies. Also, under the influence of extreme environmental factors, organisms may develop morphoses (for example, a disorder of the locomotor system due to trauma). Morphoses are irreversible and maladaptive, and in a labile nature, manifestations are similar to spontaneous mutations. Morphoses are accepted by the epigenetic theory of evolution as the main factor in evolution.

Modification variability in human life. The practical use of the patterns of modification variability is of great importance in crop and livestock production, as it allows one to anticipate and plan in advance the maximum use of the capabilities of each plant variety and animal breed (for example, individual indicators of a sufficient amount of light for each plant). The creation of known optimal conditions for the realization of the genotype ensures their high productivity. It also makes it possible to expediently use the innate abilities of the child and develop them from childhood, this is the task of psychologists and teachers who, even at school age, try to determine the inclinations of children and their abilities for one or another professional activity, increasing the level of realization of genetically determined abilities within the reaction norm children.

Examples of modification variability. In humans: an increase in the level of red blood cells when climbing mountains; an increase in skin pigmentation with intense exposure to ultraviolet rays; development of the musculoskeletal system as a result of training scars (example of morphosis).

In insects and other animals: color change in the Colorado potato beetle due to prolonged exposure to high or low temperatures on their pupae change in coat color in some mammals when weather conditions change (for example, in a hare) different colors of nymphalid butterflies (for example, Araschnia levana) that have developed at different temperatures

In plants: a different structure of underwater and emergent leaves in the water buttercup, arrowhead, etc. the development of low-growing forms from the seeds of plain plants grown in the mountains. In bacteria: the work of the genes of the lactose operon of E. coli (in the absence of glucose and in the presence of lactose, they synthesize enzymes for the processing of this carbohydrate).

Variability- the ability of living organisms to acquire new signs and properties. Through variability, organisms can adapt to changing environmental conditions.

There are two main forms of variability: hereditary and non-hereditary.

Hereditary, or genotypic, variability- changes in the characteristics of the organism due to a change in the genotype. It, in turn, is subdivided into combinative and mutational. Combinative variability arises from the recombination of hereditary material (genes and chromosomes) during gametogenesis and sexual reproduction. Mutational variability arises as a result of a change in the structure of the hereditary material.

Non-hereditary, or phenotypic, or modification, variability- changes in the characteristics of the organism, not due to a change in the genotype.

Modification variability is changes in the characteristics of organisms that are not caused by changes in the genotype and arising under the influence of environmental factors. The habitat plays an important role in the formation of the characteristics of organisms. Each organism develops and lives in a certain environment, experiencing the effect of its factors capable of changing the morphological and physiological properties of organisms, i.e. their phenotype.

An example of the variability of signs under the influence of environmental factors is the different shape of the leaves of the arrowhead: leaves immersed in water have a ribbon-like shape, leaves floating on the surface of the water are rounded, and those in the air are arrow-shaped. Under the influence of ultraviolet rays, people (if they are not albinos) develop a tan as a result of the accumulation of melanin in the skin, and the intensity of skin color is different for different people.

Modification variability is characterized by the following basic properties: 1) non-heritability;

2) the group nature of the changes (individuals of the same species, placed in the same conditions, acquire similar characteristics);

3) correspondence of changes to the action of the environmental factor;

4) dependence of the limits of variability on the genotype.

Despite the fact that signs can change under the influence of environmental conditions, this variability is not unlimited. This is due to the fact that the genotype defines specific boundaries within which a change in a trait can occur. The degree of variation of a trait, or the limits of modification variability, is called normal reaction... The reaction rate is expressed in the totality of the phenotypes of organisms that are formed on the basis of a specific genotype under the influence of various environmental factors. As a rule, quantitative traits (plant height, yield, leaf size, milk yield of cows, egg production of chickens) have a wider reaction rate, that is, they can vary widely than qualitative traits (coat color, milk fat, flower structure, blood type) ... Knowledge of the reaction rate is of great importance for agricultural practice.

Driving forces of evolution: heredity, variability, natural selection

Evolution- an irreversible process of change in a system that takes place in time, due to which something new, heterogeneous, at a higher stage of development arises, and also the imperfect dies off.

Biological evolution- This is an irreversible and, to a certain extent, directional historical development of living nature, accompanied by a change in the genetic composition of populations, the formation of adaptations, the formation and extinction of species, and the transformation of the biosphere as a whole.

Basic principles of the evolutionary theory of Charles Darwin

The essence of the Darwinian concept of evolution is reduced to a number of logical, experimentally verified and confirmed by a huge amount of factual data:

1. Within each species of living organisms, there is a huge range of individual hereditary variability in morphological, physiological, behavioral and any other characteristics. This variability can be continuous, quantitative, or intermittent qualitative, but it always exists.

2. All living organisms multiply exponentially.

3. Vital resources for any kind of living organisms are limited, and therefore there should be struggle for existence either between individuals of the same species, or between individuals of different species, or with natural conditions. Into the concept "struggle for existence" Darwin included not only the individual's own struggle for life, but also the struggle for reproductive success.

4. In conditions struggle for existence the most adapted individuals survive and give offspring, having those deviations that accidentally turned out to be adaptive to the given environmental conditions.

This is a fundamentally important point in Darwin's argumentation. Deviations do not arise directionally - in response to the action of the environment, but randomly. Few of them prove to be useful in specific conditions. The descendants of the surviving individual who inherit the beneficial deviation that allowed their ancestor to survive are more adapted to the given environment than other members of the population.

5. Survival and preferential reproduction of adapted individuals Darwin called natural selection.

6. Natural selection separate isolated varieties in different conditions of existence gradually leads to divergence (divergence) of the characteristics of these varieties and, ultimately, to speciation.

The modern evolution theory.

Darwin's main merit is that he established the mechanism of evolution that explains both the diversity of living beings and their amazing expediency, adaptation to the conditions of existence. This mechanism is a gradual natural selection of random undirected hereditary changes.

Main characteristics of modification variability

Parameter name	Meaning
Topic of the article:	Main characteristics of modification variability
Rubric (thematic category)	Genetics

1. Modification changes are not passed on from generation to generation.

2. Modification changes are manifested in many individuals of the species and depend on the effect of environmental conditions on them.

3. Modification changes are possible only within the reaction norm, that is, ultimately they are determined by the genotype.

The severity of the signs largely depends on the environment in which the organism lives.

1. High growth is determined by the genotype, that is, it is hereditary.
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Taking into account the dependence on nutritional conditions, social and living environment and vitaminization, people who inherited genes of high growth͵ are high (under optimal favorable conditions), medium (under medium conditions) and low (under bad conditions).

2. A person under the influence of ultraviolet rays predominates a protective property - sunburn (increased skin pigmentation). The degree of tanning varies from person to person. It depends on heredity, and on the intensity and duration of the factor. With the cessation of ultraviolet rays, tanning gradually disappears. And yet, there are more freckles for those who go outside a lot in sunny weather.

3. Taking into account the dependence on care, the yield of cultivated plants is different. With the observance of the entire technology of growing plants, their yield is always higher in comparison with the yield of plants cultivated in poor conditions. The degree of manifestation of decorative qualities in decorative - medicinal and decorative - flower crops directly depends on the agricultural technology of cultivation.

What conclusions can be drawn from these examples?

· The habitat plays an important role in the formation of the characteristics of organisms.

· Each organism develops and lives in a certain environment, experiencing the effect of its factors that can change the morphological and physiological properties of organisms, that is, their phenotype.

· Variability is of a non-hereditary nature, since the changes that have occurred in the parents are not transmitted to the descendants.

· A species reacts in a specific way to the action of a certain environmental factor, and the response is similar in all individuals of the same species.

The variability of organisms that occurs under the influence of environmental factors and does not affect the genotype is usually called modification.

Modification variability- variability of the phenotype; the reaction of a particular genotype to different environmental conditions.

Modification is a non-hereditary change in the phenotype that occurs under the influence of environmental factors.

Modification variability is of a group nature, that is, all individuals of the same species, placed in the same conditions, acquire similar characteristics.

Modification variability is definite, that is, it always corresponds to the factors that cause it. Thus, increased physical activity affects the degree of muscle development, but does not change the color of the skin, and ultraviolet rays change the color of the human skin, but do not change the proportions of the body.

Despite the fact that under the influence of environmental conditions, signs can change, this variability is not unlimited. Modification variability has rather rigid boundaries or limits of manifestation of a trait, determined by the genotype. The limits of modification variability of a trait of an organism call it normal reaction.

Reaction rate- the degree of variation of a trait or the limits of modification variability due to genotypes.

This means that it is not the trait as such that is inherited, but its ability to change within the normal reaction range under the influence of environmental factors. Genes determine the possibility of a trait's development, and its manifestation and severity largely determine the environmental conditions. Thus, the green color of plants depends both on genes that control chlorophyll synthesis and on the presence of light. In the absence of light, chlorophyll is not synthesized. The severity of the color of plants depends on the intensity of the light.

How can the heritability of phenotypic changes in plants be tested? In animals? (Get offspring, create other conditions for their growth and development, compare the phenotypes of parents and offspring).

The role of modification variability in nature is great, since it provides organisms with the opportunity throughout life to adapt to changed environmental conditions.

Some examples can be cited to prove this:

· Increased skin pigmentation has a protective value;

· The number of erythrocytes naturally increases with an increase in the person's residence above sea level; the need for oxygen at its low concentrations makes humans and animals adapt to respond by changing the number of erythrocytes at different heights;

· In the cold season, mammals develop a thicker and longer fur, fat accumulates actively in the subcutaneous fatty tissue, which provides thermal insulation;

· When living in cold infected areas, white hares flaunt all year in a white fur coat. And where snow is rare, the white hare does not whiten with might and main.

The norm of the body's reaction is determined by the genotype

Not the trait itself is inherited, but its ability to change within the reaction norm

· Modification variability in natural conditions is of an adaptive nature.

With hereditary (genotypic) variability, new genotypes appear, which, as a rule, leads to a change in the phenotype (recombination mutations - mutational, combinative variability).

Combinative variability consists in the fact that when two different gametes merge, new combinations of genes are formed that were not present in the original parents, which leads to the appearance of new characters.

Mutations- ϶ᴛᴏ changes in the genotype that occur under the influence of factors of the external and internal environment. For the first time the term "mutation" was proposed in 1901 by the Dutch scientist Hugo de Vries, who described spontaneous mutations in plants.

Mutational variability- ϶ᴛᴏ newly arisen changes in the hereditary structures of the cell under the influence of factors of the external or internal environment.

TYPES OF MUTATIONS

1. Gene (point) mutations(changes in genes)

1) change in the arrangement of nucleotides in DNA

2) the loss or introduction of one or more nucleotides

3) replacement of one nucleotide with another.

2. Chromosomal mutations(rearrangement of chromosomes).

1) duplication of a chromosome section (duplication)

2) loss of a portion of the chromosome (deletion)

3) moving a section of one chromosome to another, not homologous to it chromosome

4) rotation of the DNA section (inversion)

3. Genomic mutations(lead to a change in the number of chromosomes)

1) loss or appearance of new chromosomes as a result of disruption of the meiosis process

2) polyploidy - a multiple increase in the number of chromosomes.

CLASSIFICATION OF MUTATIONS

Mutations are caused by mutagens.

Mutagens- factors causing persistent hereditary changes in the body.

MUTAGENS

The main characteristics of mutational variability:

1. Mutational changes occur suddenly, and as a result, the organism acquires new properties.

2. Mutations are inherited and passed from generation to generation.

3. Mutations have no directional character, that is, it is impossible to reliably say which gene mutates under the influence of a mutagenic factor.

4. Mutations are beneficial or harmful to the body, dominant or recessive.

Hereditary variability is due to a change in the genotype.

Sources of combinative variability:

1. the process of crossing over, occurring in prophase 1 of meiosis, in which there is an exchange of sites between homologous chromosomes. The resulting recombinant chromosomes, which are in the zygote, contribute to the appearance of traits that are not characteristic of the parents.

2. the phenomenon of independent divergence of homologous chromosomes in anaphase 1 of meiosis.

3. random combination of gametes during fertilization.

All of these phenomena do not contribute to a change in the genes themselves, they only change the nature of their interaction, which leads to the emergence of a huge number of different genotypes. The resulting combinations of genes, when inherited, decay rather quickly without forming new ones.

For example, in the offspring of living organisms that stand out in one way or another, individuals appear that are inferior in these characteristics to their parents; in this regard, breeders, in order to consolidate the necessary characteristics, carry out closely related crossbreeding, in which the likelihood of meeting the same gametes increases.

Mutational variability is based on the occurrence of mutations.

Mutations - ϶ᴛᴏ a sudden change in the structure of genes, chromosomes, or the number of chromosomes. The term "mutation" was first coined by the Dutch geneticist Freese. In 1901 - 1903, on the basis of his experiments and observations, De Vries developed the mutational theory.

The main provisions of the mutation theory

1. mutations occur suddenly and intermittently.

2. mutations do not form continuous lines, they are qualitative changes.

3.mutations are useful and harmful

4. mutations are hereditary and passed down from generation to generation.

5. similar mutations can occur repeatedly.

6. mutations are undirected, since any cocus can mutate, causing changes in both minor and vital signs.

7. mutations by the nature of manifestation are dominant and recessive.

Mutational variability is characteristic of all organisms, incl. and viruses.

Breed, variety, strain- ϶ᴛᴏ artificially obtained populations of animals, plants, fungi, bacteria with traits necessary for humans.

The properties of living organisms are determined by the genotype, which is subject to hereditary variability, in this regard, the development of selection is based on the laws of genetics as the science of hereditary variability.

The task of breeding is also to improve the already existing varieties of plants, animal breeds and strains of microorganisms. The scientific foundations for the creation of new varieties of plants and animal breeds by man were revealed by Darwin in his doctrine of variability, heredity and selection.

BREEDING OBJECTIVES

The first to develop the scientific foundations of breeding work was the Russian scientist N.I. Vavilov believed that since the gene pool of the original wild fund, the success of breeding work depends on the genetic diversity of the original group of plants or animals.

As a result of numerous expeditions N.I. Vavilov and his colleagues collected a huge collection of material used for breeding work. On the basis of studying the collections of N.I. Vavilov established important regularities: different plant cultures have their centers of diversity, where the largest number of varieties, various hereditary deviations are concentrated; Cultivated plants are not equally diverse in all geographic areas. Centers of diversity are also areas of origin for varieties of a given crop.

EXERCISE. Using the text of the textbook paragraph 3.13, fill in the table "Centers of origin of cultivated plants"

CENTERS OF ORIGIN OF CULTURAL PLANTS

Center name	Geographical position	Plants
1. Indian (South Asian) Center	Hindustan Peninsula, Southern China, Southeast Asia	Tropical rice, sugarcane, banana, coconut, cucumber, eggplant, citrus
2. China (East Asian) Center	Central and Eastern China, Korea, Japan	Millet, radish, buckwheat, soy, apple, plum, cherry, a number of citrus and ornamental plants
3.Central Asian	Central Asia, Iran, Afghanistan, Northwest India	Soft wheat, peas, beans, flax, hemp, garlic, carrot, pear, apricot
4.Forest Asian Center	Turkey, the countries of the Caucasus	Rye, barley, rose, fig
5.Medium Sea Center	European, Asian and African countries located along the shores of the Mediterranean Sea	Olive, cabbage͵ parsley, sugar beet, clover
6.Abisin (Ethiopian) Center	Ethiopia, south coast of the Arabian Peninsula	Durum wheat, sorghum, bananas
7.Central American Center	Mexico, Caribbean islands, part of Central America	Corn, pumpkin, cotton, tobacco, cocoa, red pepper
8 South American (Andean) Center	West coast of South America	Potatoes, pineapple, peanuts, cinchona, tomato, beans

The analysis of a huge number of cultivated plants and their wild-growing ancestors allowed N.I. Vavilov to formulate the law of homologous series of hereditary variability:

This law makes it possible to predict the existence of wild plants with traits that are valuable for breeding work.

All modern plant varieties and animal breeds, without which modern civilization is inconceivable, were created by man through selection.

- grade- a set of cultivated plants of one species, artificially created by man and characterized by certain hereditary characteristics: productivity, morphological and physiological characteristics.

- Breed - a set of domestic animals of the same species, artificially created by man and characterized by certain hereditary characteristics: duration, exterior.

- Strain - a set of microorganisms.

From the definition of selection, it is clear that the purpose of the practice of breeders is to create new varieties of plants, animal breeds and strains of microorganisms that have the qualities necessary for humans.

Breeding tasks:

1. increasing the productivity of varieties and productivity of breeds.

2. improving product quality.

3. increasing resistance to diseases, pests.

4. ecological plasticity of varieties and breeds.

5. suitability for mechanized and industrial cultivation and breeding.

The pioneer in the development of the scientific foundations of breeding work in our country was N.I. Vavilov. He believed that the basis of selection is the correct choice for the work of the source material, their genetic diversity and the influence of the environment on the manifestation of hereditary traits during the hybridization of individuals.

In search of source material for obtaining new plant hybrids, NI Vavilov organized dozens of expeditions around the globe in the 1920s and 1930s.

Consider the centers of origin of cultivated plants:

The study of the origin of cultivated plants led Vavilov to the conclusion that the centers of formation of the most important cultivated plants are largely associated with the centers of human culture and the centers of diversity of domestic animals.

Vavilov, studying hereditary variability in cultivated plants and their wild ancestors, discovered a number of regularities that made it possible to formulate the law of homologous series of hereditary variation: genetically close genera and species are characterized by similar series of hereditary variability with such accuracy that knowing a number of forms within one species, one can foresee the finding of parallel forms in other related species and generaʼʼ.

The main directions of Vavilov's scientific work:

1.forming the tasks of modern breeding

2.creation of the doctrine of the centers of diversity and origin of cultivated plants

3.the law of homologous series

4.development of the problem of plant immunity

5.creation of a collection of seeds of cultivated plants and their wild-growing ancestors

6. Creation of a network of institutes and selection experimental stations in the country.

The main characteristics of modification variability are the concept and types. Classification and features of the category "Main characteristics of modification variability" 2017, 2018.