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The study of both experimental and theoretical consequences of mendelian heredity on the population level, in contradistinction to classical genetics which deals with the offspring of specified parents on the familial level. The genetics of populations studies the frequencies of genes, genotypes, and phenotypes, and the mating systems. It also studies the forces that may alter the genetic composition of a population in time, such as recurrent mutation, migration, and intermixture between groups, selection resulting from genotypic differential fertility, and the random changes incurred by the sampling process in reproduction from generation to generation. This type of study contributes to an understanding of the elementary step in biological evolution. The principles of population genetics may be applied to plants and to other animals as well as humans. See Genetics, Mendelism
a branch of genetics that studies the genetic structure and dynamics of the genetic makeup of populations. Changes in the frequency of individual genes and genotypes in populations are caused by mutations, the nature of crossings within a population, interpopulation migrations, random fluctuations, and natural selection, the unique directing factor of evolution.
These factors become more significant under natural conditions because of their interaction. S. S. Chetverikov of the USSR, R. Fisher and J. Haldane of Great Britain, and S. Wright of the United States pioneered in the creation and development of population genetics in the 1920’s and 1930’s.
Work in experimental population genetics was begun in 1926 by Chetverikov, who theoretically forecast the enormous genetic heterogeneity of natural populations and suggested methods of studying it. The prevalence in populations of heterozygotes for different types of mutations and of structurally changed chromosomes was demonstrated by Chetverikov’s school in the USSR, by T. Dobzhansky’s school in the United States, and by many other investigators. According to modern estimates, 10 to 30 percent of the genes in natural populations consist of two or more alleles. From the evolutionary standpoint, genetic heterogeneity—that is, the accumulation of hereditary variations by a population—is a peculiar “mobilization reserve” (I. I. Shmal’gauzen) used by a population during gradual or sudden changes in environmental conditions. Populations with greater genetic variety usually are more abundant and have higher birthrates. However, genetic heterogeneity also results in the accumulation of genetic load or of genes that diminish the viability and fecundity of homozygotes, causing a decrease in the average adaptability of the population. Some populations have been found to possess high frequencies of mutations of different kinds, as high as 30 or 40 percent. This may be related to the greater relative viability of the heterozygotes, change in the adaptability of various genotypes by seasons, and the dependence of the viability of a given genotype on the density and genotypic composition of the population.
Major areas of study in modern population genetics include genetic heterogeneity, the genetic load of a population, polymorphism, and the relation of these phenomena to ecological factors. Mathematical population genetics, which was founded in 1908 by the British mathematician G. Hardy, is progressing rapidly. Mathematical models are now widely used in population genetics; their construction and analysis help identify and precisely formulate the main problems of experimental research and sometimes aid in providing qualitative or even quantitative solutions. Computers are used to construct models used in studying complex population systems.
The development of population genetics has enabled scientists to understand the principal mechanisms of speciation. Population genetics is closely related to research in anthropology, medical genetics, and the breeding of animals, plants, and microorganisms. It provides the scientific basis for preserving and making efficient use of the gene pool of living organisms on earth.
REFERENCESChetverikov, S. S. “O nekotorykh momentakh evoliutsionnogo protsessa stochki zreniia sovremennoi genetiki.” Zhurnal eksperimental’noi biologii: Ser. A, 1926, vol. 2, issue 1.
Haldane, J. B. S. Faktory evoliutsii. Moscow-Leningrad, 1935. (Translated from English.)
Dubinin, N. P. Evoliutsiia populiatsii i radiatsiia. Moscow, 1966.
Mettler, L., and T. Gregg. Genetika populiatsii i evoliutsiia. Moscow, 1972. (Translated from English.)
Timofeev-Resovskii, N. V., A. V. Iablokov, and N. V. Glotov. Ocherk ucheniia o populiatsii. Moscow, 1973.
Fisher, R. A. The Genetical Theory of Natural Selection, 2nd ed. New York, 1958.
Dobzhansky, T. Genetics of the Evolutionary Process. New York-London, 1970.
Wright, S. Evolution and the Genetics of Populations, vols. 1–3. Chicago-London, 1969–70.
N. V. GLOTOV