withinpopulation

Withinpopulation refers to the genetic variation and demographic processes that occur among individuals within a single population. In population genetics, it is contrasted with between-population variation, which describes differences among separate populations. Within-population diversity is commonly quantified with measures such as expected heterozygosity (He), observed heterozygosity (Ho), and nucleotide diversity (π). Measures of population structure, like FIS (inbreeding within a population) and FST (genetic differentiation among populations), are used to partition genetic variance into within- and between-population components; analyses of molecular variance (AMOVA) implement this partitioning.

Factors shaping within-population variation include mutation, recombination, natural selection, genetic drift, gene flow, and demographic factors such as census and effective population size, mating system, and population history. Generally, larger populations with higher gene flow maintain greater within-population variation, while small, isolated populations are more affected by drift and can accumulate inbreeding, reducing within-population diversity.

Applications of within-population analyses include conservation genetics, where levels of within-population diversity inform management decisions and inbreeding risk; evolutionary biology, where within-population variation affects adaptive potential; and human genetics, where most genetic variation is found within populations rather than between them, a pattern that informs studies of ancestry and disease.