 Analysing the consequences of non-random mating gets quite complicated, but some conclusions are fairly easily seen. Firstly, non-random mating does not in itself affect gene frequencies (so arguably is not an evolutionary ‘force’ on a par with selection, mutation and migration); rather, it affects genotype frequencies. To appreciate this point, note that the gene frequency of a population, at the zygotic stage, is equal to the gene frequency in the pool of successful gametes from which the zygotes are formed. The pattern of mating simply determines the way in which haploid gametes are ‘packaged’ into diploid zygotes. Thus if a random mating population suddenly starts to mate non-randomly, this will have no effect on gene frequencies.