Mutations that occur naturally without affecting the body of various factors are called spontaneous. Main Feature manifestations of spontaneous mutations is that genetically close species and genera are characterized by the presence of similar forms of variability. The pattern of the presence of homologous series in hereditary variability was established by the outstanding geneticist and breeder, Academician N.I. Vavilov (1920). He found that homologous series exist not only at the species and genus levels in plants, but can also be found in mammals and humans.
The essence of the law is that genetically close genera and species are characterized by homologous (similar) series in hereditary variability. Similar genotypic variability is based on a similar genotype in closely related forms (i.e., a set of genes, their position in homologous loci). Therefore, knowing the forms of variability, for example, a number of mutations in species within the same genus, one can assume the presence of the same mutations in other species of a given genus or family. Similar mutations in genetically related species N.I. Vavilov called homologous series in hereditary variability. Examples:
1) representatives of the cereal family have a similar genotype. Similar mutations are observed within the genera of this family (wheat, rye, oats, etc.). These include the following: naked-grained, awnless, lodging, different consistency and color of grain, etc. Awnless forms of wheat, rye, oats, and rice are especially common;
2) similar mutations occur in humans and mammals: short-toed (sheep, humans), albinism (rats, dogs, humans), diabetes(rats, humans), cataracts (dogs, horses, humans), deafness (dogs, cats, humans), etc.
The law of homological series of hereditary variability is universal. Medical genetics uses this law to study diseases in animals and develop treatments for them in humans. It has been established that oncogenic viruses are transmitted through germ cells, integrating into their genome. At the same time, the offspring develop comorbidities similar to those of the parents. The DNA nucleotide sequence has been studied in many closely related species, and the degree of similarity is more than 90%. This means that the same type of mutations can be expected in related species.
The law has wide application in plant breeding. Knowing the nature of hereditary changes in some varieties, it is possible to predict similar changes in related varieties by acting on them with mutagens or using gene therapy. In this way, beneficial changes can be brought about in them.
Modification variability(according to Ch. Darwin - a certain variability) - is a change in the phenotype under the influence of environmental factors that are not inherited, and the genotype remains unchanged.
Changes in the phenotype under the influence of environmental factors in genetically identical individuals are called modifications. Modifications are otherwise called changes in the degree of expression of a trait. The appearance of modifications is due to the fact that environmental factors (temperature, light, moisture, etc.) affect the activity of enzymes and, within certain limits, change the course of biochemical reactions. Modification variability is adaptive in nature, in contrast to mutational variability.
Modification examples:
1) the arrowhead has 3 types of leaves, which differ in shape, depending on the action of the environmental factor: arrow-shaped, located above the water, oval - on the surface of the water, linear - immersed in water;
2) in a Himalayan rabbit, in place of shaved white wool, when it is placed in new conditions (temperature 2 C), black hair grows;
3) when using certain types of feed, body weight and milk yield of cows increase significantly;
4) lily of the valley leaves on clay soils wide, dark green, and on poor sandy ones - narrow and pale in color;
5) Dandelion plants relocated high up in the mountains, or in areas with a cold climate, do not reach normal sizes, and grow dwarfed.
6) with an excess content of potassium in the soil, plant growth increases, and if there is a lot of iron in the soil, then a brownish tint appears on the white petals.
Mod properties:
1) modifications can occur in a whole group of individuals, because these are group changes in the severity of signs;
2) the changes are adequate, i.e. correspond to the type and duration of exposure to a certain environmental factor (temperature, light, soil moisture, etc.);
3) modifications form a variation series, therefore they are referred to as quantitative changes in features;
4) modifications are reversible within one generation, i.e. with a change in external conditions in individuals, the degree of expression of signs changes. For example, in cows with a change in feeding, milk yield may change, in humans, under the influence of ultraviolet rays, a tan, freckles, etc. appear;
5) modifications are not inherited;
6) modifications are adaptive (adaptive) in nature, i.e., in response to changes in environmental conditions, individuals exhibit phenotypic changes that contribute to their survival. For example, domestic rats adapt to poisons; hares change seasonal color;
7) are grouped around the average value.
Under the influence of the external environment, to a greater extent, the length and shape of the leaves, height, weight, etc.
However, under the influence of the environment, signs can change within certain limits. reaction rate are the upper and lower bounds within which the attribute can change. These limits, in which the phenotype can change, are determined by the genotype. Example 1: milk yield from one cow is 4000–5000 l / year. This indicates that the variability of this trait is observed within such limits, and the reaction rate is 4000–5000 L/year. Example 2: if the height of the stem of a tall oat variety varies from 110 to 130 cm, then the reaction rate of this trait is 110–130 cm.
Different signs have different norms of reaction - wide and narrow. Wide reaction rate- leaf length, body weight, milk yield of cows, etc. Narrow reaction rate- the fat content of milk, the color of seeds, flowers, fruits, etc. Quantitative signs have a wide reaction rate, and qualitative ones have a narrow reaction rate.
Statistical analysis of modification variability on the example of the number of spikelets in an ear of wheat
Since modification is a quantitative change in a trait, it is possible to perform a statistical analysis of modification variability and derive the average value of modification variability, or a variation series. Variation series variability of the trait (i.e., the number of spikelets in the ears) - the arrangement in a row of ears according to the increase in the number of spikelets. The variational series consists of separate variants (variations). If we count the number of individual variants in the variation series, we can see that the frequency of their occurrence is not the same. Options ( variations) is the number of spikelets in ears of wheat (single expression of the trait). Most often, the average indicators of the variation series are found (the number of spikelets varies from 14 to 20). For example, in 100 ears, you need to determine the frequency of occurrence different option. According to the results of calculations, it can be seen that most often there are spikes with an average number of spikelets (16–18):
The top row shows the options, from smallest to largest. The bottom row is the frequency of occurrence of each option.
The distribution of a variant in a variation series can be shown visually using a graph. The graphical expression of the variability of a trait is called variation curve, which reflects the limits of variation and the frequency of occurrence of specific variations of the trait (Fig. 36) .
V
Rice. 36 . Variation curve of the number of spikelets in an ear of wheat
In order to determine the average value of the modification variability of wheat ears, it is necessary to take into account the following parameters:
P is the number of spikelets with a certain number of spikelets (the frequency of occurrence of the trait);
n is the total number of series options;
V is the number of spikelets in an ear (options forming a variational series);
M - the average value of modification variability, or the arithmetic mean of the variation series of ears of wheat is determined by the formula:
M=–––––––––– (average value of modification variability)
2x14+7x15+22x16+32x17+24x18+8x19+5x20
M=––––––––––––––––––––––––––––––––––––––– = 17, 1 .
average value modification variability has a practical application in solving the problem of increasing the productivity of agricultural plants and animals.
Homologous series in hereditary variability law, open Russian geneticist N.I. Vavilov in 1920 established a pattern establishing parallelism (similarity) in hereditary (genotypic) variability in related organisms. In Vavilov's formulation, the law reads: "Species and genera that are genetically close to each other are characterized by identical series of hereditary variability with such regularity that, knowing the series of forms for one species, one can foresee the finding of identical forms in other species and genera." At the same time, the closer the relationship between species, the more complete the similarity (homology) in the series of their variability. The law summarizes a huge amount of material on the variability of plants (cereals and other families), but it turned out to be true for the variability of animals and microorganisms.
The phenomenon of parallel variability in closely related genera and species is explained by their common origin and, consequently, by the presence of a large part of the same genes in them, obtained from a common ancestor and not changed in the process. When mutated, these genes give similar traits. Parallelism in genotypic variability in related species is manifested by parallelism in phenotypic variability, i.e., similar characters (phenotypes).
Vavilov's law is the theoretical basis for choosing directions and methods for obtaining economically valuable traits and properties in cultivated plants and domestic animals.
In 1920 N.I. Vavilov presents the main ideas of the Law of Homological Series in a report at the III All-Russian Breeding Congress in Saratov. main idea: related plant species have similar spectra of variability (often a fixed number of well-defined variations).
“And Vavilov did such a thing. He collected all known hereditary traits from the best studied, as I have already said, plants from among cultivated cereals, arranged them in a certain order in tables and compared all subspecies, forms and varieties known to him at that time. There were many tables compiled, of course, the material was huge. At the same time, back in Saratov, he fastened legumes to cereals - various peas, vetch, beans, beans, etc. - and some other crops. And it turned out in very many cases parallelism in very many species. Of course, for each family, genus, and species of plants, all signs had their own characteristics, their own form, their own way of expression. For example, seed color from almost white to almost black varied in almost all cultivated plants. This means that if better-studied cereals with a huge number of already known, studied varieties and forms have several hundred different traits, while other, less studied or wild relatives of cultivated species do not have many traits, then they can, so to speak, be predicted. They will still be found on the corresponding large material.
Vavilov showed that, on the whole, the hereditary variability of all plants varies in parallel to a very strong degree. He called it the homologous series of plant variability. And he pointed out that the closer the species are to each other, the greater this homology of the series of variability of characters. Whole line different general regularities was revealed on these homologous series of hereditary variability of plants. And this circumstance was taken by Vavilov as one of the most important foundations for further selection and the search for economically useful traits in plants introduced into cultivation. The study of homologous series of hereditary variability, first of all in cultivated plants, then in domestic animals, is now a matter of course, one of the foundations of further selection. necessary to a person varieties of certain species of plants under study. This was, perhaps, one of the first major achievements of Vavilov on a world scale, which very quickly created him a world name. The name, if not the first and best, then one of the first and best applied botanists in the world.
In parallel with this, Vavilov made a large number of expeditions around the world - throughout Europe, most of Asia, a large part of Africa, North, Central and South America - collecting huge material, mainly on cultivated plants. In 1920, I think, Vavilov was made director of the Bureau of Applied Botany and New Cultures. This Bureau was somewhat changed and turned into the Institute for Applied Botany and New Crops, then the Institute for Applied Botany, Genetics and Plant Breeding. And by the end of the 1930s, it had already become the All-Union Institute of Plant Growing. This name has been preserved to this day, although its global share, of course, fell sharply after the death of Vavilov. But still, many Vavilov traditions are still maintained, and part of the huge world living collection of varieties, subspecies and forms of cultivated plants from literally all groups of plants cultivated on the globe is preserved in Pushkin, the former Detskoye Selo, the former Tsarskoye Selo. This is a living museum, replanted every year, created by Vavilov. The same is true at countless experimental stations scattered throughout the Soviet Union.
During his many trips, Vavilov again managed not to drown in a huge amount of material, in this case already a geographical variety of forms. various kinds cultivated plants. He marked everything on large-scale maps with colored pencils, at first playing, like little children, at geographic Maps, and then translating all this into relatively simple small cards with black icons various types for different forms of cultivated plants. So he discovered in the world, on the globe, in the biosphere of our planet, several centers of diversity of cultivated plants. And he showed, simply on maps, the spread, distribution on Earth not only of individual species, but of certain groups of species, cultivated, apparently, for the first time in a certain place, let's say, in Northern or Central China or in the mountainous part of North Africa, or , say, in the region of Peru, in South America, in the mountains, in the Andes. From there, usually not one species of any cultivated plants, but a group of economically connected species that arose as cultivated plants and took root as cultivated plants in a certain place, spread over the Earth. Some are not far, a short distance, while others have conquered half the world, as they say, like the same wheat or peas.
Vavilov, thus, established the centers of diversity and origin of various forms of cultivated plants in different parts of the globe. And he created a whole theory of the origin of cultivated plants in various eras of the most ancient and ancient world. This was Vavilov's second great achievement, again world-class. Impossible now further development the history of world agriculture and the history of the centers of origin of cultivated plants without the foundation created by Vavilov. There are attempts, so to speak, of some reform and modification of Vavilov's views, but we can say that these are particulars in comparison with the general world picture created by Vavilov.
This means that I have already listed three great achievements: plant immunity, the law of homological series, and the theory of centers of agriculture and the emergence of various forms of cultivated plants. Perhaps the last thing I want to name from Vavilov’s overall achievements is a large number of his works and efforts, mainly efforts, already in the sense of propaganda at various congresses, international and all-Union, writing popular science articles on the problem of advancing agriculture to the north in the first place and in the areas occupied by deserts and wastelands, combined with the protection of nature in a completely modern and even intended for the near future sense: the promotion of culture along with a reasonable attitude towards the communities of living organisms of the biosphere. In these areas, Vavilov is absolutely exceptional, I would say, an exceptionally great scientist on a global scale.
The processing of extensive material of observations and experiments, a detailed study of the variability of numerous Linnaean species (Linneons), a huge amount of new facts obtained mainly from the study of cultivated plants and their wild relatives, allowed N.I. Vavilov to bring everything into a single whole notable examples parallel variability and formulate common law, called by him "The law of homological series in hereditary variability" (1920), reported by him at the Third All-Russian Congress of Breeders, held in Saratov. In 1921 N.I. Vavilov was sent to America for the International Congress on agriculture, where he made a presentation on the law of homologous series. The law of parallel variability of closely related genera and species, established by N.I. Vavilov and associated with a common origin, developing the evolutionary teachings of Charles Darwin, was duly appreciated by world science. It was perceived by the audience as the largest event in the world biological science, which opens up the widest horizons for practice.
The law of homological series, first of all, establishes the foundations of the taxonomy of the huge variety of plant forms that the organic world is so rich in, allows the breeder to get a clear idea of the place of each, even the smallest, systematic unit in the plant world and judge the possible diversity of the source material for selection.
The main provisions of the law of homological series are as follows.
"one. Species and genera that are genetically close are characterized by similar series of hereditary variability with such regularity that, knowing the number of forms within one species, one can foresee the occurrence of parallel forms in other species and genera. The closer genetically located in common system genera and linneons, the more complete is the similarity in the series of their variability.
2. Whole families of plants are generally characterized by a certain cycle of variability passing through all the genera and species that make up the family.
Even at the III All-Russian Congress on Selection (Saratov, June 1920), where N.I. Vavilov reported his discovery for the first time, all participants of the congress recognized that “like the periodic table (periodic system)” the law of homological series will allow predicting the existence, properties and structure of still unknown forms and species of plants and animals, and highly appreciated the scientific and practical value of this law. Modern advances in molecular cell biology make it possible to understand the mechanism of the existence of homological variability in similar organisms - on what exactly the similarity of future forms and species with existing ones is based - and to meaningfully synthesize new forms of plants that are not found in nature. Now a new content is being introduced into Vavilov's law, just as the advent of quantum theory has given a new, deeper content to Mendeleev's periodic system.
Activities of N. I. Vavilov
The outstanding Soviet geneticist Nikolai Ivanovich Vavilov made a great contribution to the development of domestic science. A whole galaxy of prominent Russian scientists was brought up under his leadership. The studies carried out by N.I. Vavilov and his students made it possible for agricultural science to master new methods of searching for wild plant species as a starting material for breeding, laid the theoretical foundations of Soviet breeding.
Remark 1
Based on the huge amount of collected collection material, the doctrine of the centers of origin of cultivated plants was formulated. And the seed samples collected by Vavilov and his associates provided a wide front for genetic research and breeding work.
It was thanks to the analysis of the collected materials that the famous law of homological series was formulated.
The essence of the law of homologous series of hereditary variability
In the course of a long-term study of wild and cultivated forms of vegetation on five continents, N.I. Vavilov concluded that the variability of species and genera close in origin occurs in similar ways. In this case, the so-called series of variability are formed. These series of variability are so correct that, knowing a number of characters and forms within one species, one can foresee the presence of these qualities in other species and genera. The closer the relationship, the more complete the similarity in the series of variability.
For example, in watermelon, pumpkin and melon, the shape of the fruit can be oval, round, spherical, cylindrical. The color of the fruit may be light, dark, striped or spotted. The leaves of all three plant species can be entire or deeply dissected.
If we consider cereals, then out of $38$ of the studied traits characteristic of cereals:
- $37 was found in rye and wheat,
- barley and oats - $35$,
- for corn and rice - $32$,
- millet has $27.
Knowledge of these regularities makes it possible to foresee the manifestation of certain traits in some plants. On the example of the manifestation of these signs in other plants related to them.
In the modern interpretation, the formulation of this law of homological series of hereditary variability is as follows:
“Related species, genera, families have homologous genes and gene orders in chromosomes, the similarity of which is the more complete, the evolutionarily closer compared taxa.”
Vavilov established this regularity for plants. But subsequent research has shown that the law is universal.
The genetic basis of the law of homologous series of heredity
The genetic basis of the above-mentioned law is the fact that under similar conditions, closely related organisms can react in the same way to environmental factors. And their biochemical processes proceed in approximately the same way. This pattern can be formulated as follows:
“The degree of historical commonality of organisms is directly proportional to the number common genes groups that are being compared.
Since the genotype of closely related organisms is similar, the changes in these genes during mutations can be similar. Outwardly (phenotypically), this manifests itself as the same character of variability in closely related species, genera, etc.
The meaning of the law of homologous series of heredity
The law of homological series is of great importance both for the development of theoretical science and for practical application in agricultural production. It gives the key to understanding the direction and ways of evolution of related groups of living organisms. In breeding, on its basis, they plan to create new varieties of plants and breeds of domestic animals with a certain set of characteristics, based on the study of the hereditary variability of related species.
In the taxonomy of organisms, this law makes it possible to find new expected forms of organisms (species, genera, families) with a certain set of features, provided that such a set was found in related systematic groups.
