Assortative mating

Assortative mating is the non-random selection of mates with respect to one or more traits. Negative assortative mating is the preferential selection of mates with different genotypes; positive, with similar. Both forms of assortative mating act against Hardy-Weinberg equilibrium as they increase the frequency of homozygosity, both for the trait allele(s) and any alleles that are in linkage disequilibrium with those alleles.