Give three processes that may cause a population's genotype frequencies to deviate from Hardy-Weinberg?

1. Non-random mating - individuals prefer to mate with others like themselves for example rather than at random, so if you have birds with blue feathers and purple feathers that prefer their own kind this will cause a lack of heterozygotes with both alleles.

2. Natural selection - If one of the genotypes in the population is less fit than the others selection will reduce it and therefore the allele combination that produces it - e.g. genetic disease.

3. Migration - the arrival of new alleles in the population each generation will change the allele frequencies so no equilibrium is established.