Mating Systems Which Could Increase Heterozygosity for a Pair of Alleles

If neither of two alleles at a locus is dominant, mating biases could cause the frequency of heterozygotes to rise above that under random mating. If homozygotes mate with unlike homozygotes and heterozygotes with heterozygotes, allelic frequencies equalize and eventually 2/3 of the population becomes heterozygotic. If mating is random except that unlike homozygotes do not mate, then again allelic frequencies equalize but heterozygosity at equilibrium is 0.554958. These systems could complement selection for heterozygotes or have other adaptive value. Two related but less likely systems are also discussed.