Population Structure and Gene Flow

Abstract

Population genetics is chiefly concerned with finding out the origin, population structure, and demographic history of a species. Intra- and interpopulation genetic variation elucidates the pattern of species origin and demography. Natural populations display geographic population substructure, which is the function of genetic differences in populations from different geographic regions. Natural populations invariably show substructuring as herds, flocks, colonies, etc., due to random mix of favorable areas with the unfavorable ones. Population subdivision leads to genetic differentiation among the subpopulations as they acquire variable allele frequencies that vary among the subpopulations. Population subdivision is centrally important for evolution and affects estimation of all evolutionary parameters from natural and domestic populations. In subdivided populations, random genetic drift (cause of genetic divergence among subpopulations) acts antagonistically to migration, which holds a subpopulation together, and the balance between the two decides the degree of genetic divergence that can occur. As an evolutionary process that brings potentially new alleles into a population, migration is qualitatively similar to mutation. The major difference is quantitative, i.e., the rate of migration among subpopulations of a species is higher than the rate of mutation of a gene.