Practice question

Hardy-Weinberg equilibrium describes an ideal, non-evolving diploid sexual population where allele and genotype frequencies remain constant across generations. Classical assumptions include infinitely large population size to eliminate drift, random mating ensuring random gamete union, absence of new mutations, absence of migration causing gene flow, and absence of natural selection so all genotypes have equal fitness. Directional selection systematically favors one allele over another, steadily shifting p and q. Because it changes allele frequencies, it violates equilibrium and therefore represents the exception among listed conditions that maintain stability.