Population genetics

Population genetics is the branch of genetics that studies inheritance processes within biological populations. It determines the relative frequency of homologous genes (alleles) in populations (gene frequency) and investigates their change under the influence of mutation, selection, random gene drift, the separation of subpopulations and gene flow between populations. It is of great importance in evolutionary research and in animal and plant breeding.

An important principle of population genetics is the Hardy-Weinberg law, independently discovered as early as 1908 by Wilhelm Weinberg and Godfrey Harold Hardy, which describes a state of equilibrium in purely random mating and in the absence of any selection, in which the frequency of alleles of a gene remains constant from generation to generation.

Population genetics became established as an independent branch of research in the 1920s, after Reginald Punnett had introduced Weinberg's and Hardy's discovery, which had previously gone almost unnoticed, into population biology as "Hardy's law" in 1917. The founders of this new branch of research were Sewall Wright, Ronald A. Fisher, and J. B. S. Haldane. In the 1930s and 1940s, population genetics made a significant contribution to the unification of the theory of evolution founded by Charles Darwin and the genetics of Gregor Mendel in the synthetic theory of evolution, which is still valid today, by helping to resolve the contradictions that existed between these theories.

The Hardy-Weinberg equilibrium is a theoretical construct to which no real population corresponds. In real populations, various mechanisms of selection are at work, which favour certain alleles over others. However, except in very small populations, this does not lead to the sole retention of the "fittest" genotype, but a certain diversity (polymorphism) always remains. The numerous reasons for this are also the subject of population genetics research. One of them is the frequently observed phenomenon of heterosis, which consists in the fact that heterozygous individuals are preferred by selection over homozygous individuals, i.e. they prove to be fitter. Conversely, inbreeding, i.e. the mating of genetically closely related or identical individuals, proves to be disadvantageous, which is due in particular to the increased occurrence of recessive genes.