From Big Medical Encyclopedia

POPULATION GENETICS (late lat. populatio, from armor. populus people, population; genetics) — the section of genetics devoted to studying of patterns of variability and heredity at the level of population.

As the independent section P. of it was created at the beginning of 20 century. In 1903 Mr. W. L. Johannsen published work «About inheritance in populations and pure lines». In 1908 Hardy (G. N of Hardy) and W. Weinberg gave mathematical justification of a ratio of alleles in population (see. Population, genetics of population ). In 1926 S. S. Chetverikov showed that genotypic evolution of populations define accumulation of mutations (see. Mutation ) and natural selection (see), in 1929 it published results of the first pilot study on genetics of natural populations. In 1931 — 1932 N. P. Dubinin, D. D. Romashov and S. Wright formulated the theory of genetikoavtomatichesky processes (the theory of drift of genes). Establishment of four major factors defining patterns of variability and heredity in populations was result of all these researches: 1) mutations of genes and chromosomes (see. Mutation ); 2) the selection providing differential reproduction of individuals in population; 3) the drift of genes bringing in conditions of isolation to changes of concentration of alleles (see. Isolates ); 4) the migrations (mixing) of populations leading to alignment of concentration of alleles (see. Variability , Heredity ).

The individuals divided into populations keep a possibility of crossing with other individual of this look that provides its integrity. Strong impact on genetic structure of population is exerted by accidental deviations in structure alleles (see) which arise in small group of individuals at settling of new places by them. Maier (E. Mayer) called this phenomenon «the principle of founders». Migrations of individuals from one population in another lead to alignment of genetic distinctions between populations, isolation, on the contrary, promotes their genetic differentiation. Distribution of many alleles at the person is caused by mixing of populations. E.g., in the USA exchange of genes which for the last two centuries happened preferential from white to Blacks led to what to the second half of 20 century Blacks have already apprx. 30% of genes of the white person.

Opening by N. P. Dubinin in 1931 — 1934 of recessive lethal mutations in populations of a drosophila laid the foundation for the doctrine about a genetic load of populations. This load develops of lethal, semi-legal and sublethal changes and can be segregatsionny, i.e. be shown by «vyshchepleniye» of less adapted homozygotes in the presence in population of selection in favor of heterozygotes, or can be mutational, i.e. be shown in populations by the mutations reducing fitness of individuals, carriers of these mutations. There is a so-called load of drift — accidental increase in concentration of alleles in the isolated population. Private result of such load is increase in a share of homozygous individuals at inbreeding (see) — a so-called inbredny load or an inbredny depression.

The volume of a genetic load is defined by a variety of the mutations which are available in population. Increase in concentration of mutations restrains selection therefore each recessive mutation is included in a gene pool of population at a low level. However total number of recessive mutations is so big that each person bears, e.g., 3 — 4 lethal mutations.

If in population there is a change of concentration of alleles, then distribution of genotypes at the new level is established already in the next generation on the basis of laws of free crossing. In 1948 N. P. Dubinin showed that the condition of population is connected with genetic polymorphism (see). The complex of genes, in charge of adaptive properties of an organism, is presented by closely linked group of genes (the block of the genes) localized on limited sites of chromosomes in to-rykh is complicated recombination (see). Thus, in populations in the course of evolution there is an integration of the whole gene systems providing fitness of normal phenotypes to these conditions of the environment. It is offered to call such integrated systems of genes creating a large supply of genotypic variability koadaptirovanny complexes of genes or supergenes. The general system of koadaptirovanny genes is dynamic as it develops of their complexes. It allows it to be reconstructed according to changes of the environment and to have «memory» about ekol, conditions of the habitat of population. In more detail see. Population, genetics of population .

See also Genetics .

Bibliography: Dubinin N. P. Evolution of populations and radiation, M., 1966; L evontin R. K. Genetic bases of evolution, the lane with English, M., 1978; JI and H. Introduction to population genetics, the lane with English, M., 1978, bibliogr.; Mettler L. Yu. and Gregg T. G. Genetics of populations and evolution, the lane with English, M., 1972; P about to and c to and y P. F. Introduction to statistical genetics, Minsk, 1978; Chetverikov S. S. About some moments of evolutionary process from the point of view of modern genetics, in book: Classics of owls. geneticists, under the editorship of H. M. Zhukovsky, page 133, L., 1968; Sheppard F. M. Natural selection and heredity, the lane with English, M., 1970; Crow J. F. and. To i m u of and M. Ap of introduction to population genetics theory, N. Y., 1970; Dobzhansky Th. Genetics of the evolutionary process, N. Y., 1970; Ford E. B. Ecological genetics, L., 1971.

H. P. Dubinin.