Genetics - A. V. Sivolob 2008

Population Genetics
Factors of the Dynamics of Population Genetic Structure
Migrations

Migration, or Gene flow between populations, increases intra-population variation while reducing genetic divergence among populations. This process alters both allele and genotype frequencies. The magnitude of these changes depends on population sizes and migration rates.

Let us consider a recipient population into which individuals from donor populations migrate at a specific rate. We assume that the population size remains constant, immigrants freely interbreed with residents, and all individuals exhibit equal viability.

Suppose that in the recipient population, the initial (pre-migration) frequency of allele A is p0, while in the donor population it is pd. Let m denote the proportion of migrants. Consequently, in the gene pool of the next generation, the fraction of genes derived from migrants will be m, and from residents — (1 - m). After one generation of migration (immigration), the allele frequency in the recipient population will be

p1 = (1 - m)po+ mpd= po - m(po - pd), and The change in allele frequency resulting from migration over a single generation is

Class="center">∆p = p1 - po = - m(po - pd).

The allele frequency in the recipient population will continue to change until migration ceases (m = 0) or until allele frequencies equalize between the populations (po = pd). Following one generation of migration, the difference in allele frequencies between the two populations becomes

p1 - pd = (1 - m)(po - pd).

After two generations, this difference will decrease to

p2- pd= (1 - m)2(po- pd),

and after t generations,

pt- pd= (1 - m)t(po- pd).

This final formula allows us to predict changes in allele frequency within a population over a given time following the onset of migration, provided the migration rate m is known. It should be noted that this Structure/133.html">Discussion specifically concerns immigration; emigration from a population (assuming non-selective emigration with respect to genotypes—i.e., random and proportional to genotype frequencies) will not alter allele frequencies.



Last update: 11/08/2026

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