No matter how many generations' alleles are segregated by meiosis and combined by fertilization, the frequencies of the alleles in the gene pool will remain constant unless acted on by other agents . The population must be isolated . There must be no migration of individuals into or out of the population. There are no net changes to alleles due to mutations . Mating is random .
All genotypes are equal in reproductive success .
Whilst these conditions can be approached in nature, they are never achieved for very long . Back to the top of this page Population Genetics Population genetics is the scientific study of gene pools and the genetic variation within populations. Because the five conditions for Hardy-Weinberg equilibrium are seldom maintained for many generations, gene frequencies in gene pools do change . If a population is small, genetic drift may occur. Chance events in matings may cause the allele frequencies to drift randomly from generation to generation .