Genotype frequencies depend on allele frequencies and the breeding pattern in the population. Frequencies of specific matings are determined by genotype frequencies and the breeding pattern in the population. The proportion of an allele found in heterozygotes is maximal when the allele is rare. Inbreeding shifts the equilibrium in favour of homozygotes. Allele frequency can be changed by mutation, selection, drift, migration and founder effects.
Constant mutation changes allele frequency very slowly.
Selection against a rare recessive changes allele frequency very slowly. When mutation and selection act in opposite directions an equilibrium allele frequency is attained.