What typically happens in a population under Hardy-Weinberg equilibrium?

In a population under Hardy-Weinberg equilibrium, the key aspect is the stability of allele and genotype frequencies over time. This equilibrium represents a theoretical state where five essential conditions are met: no mutations, random mating, no natural selection, extremely large population size (which mitigates effects of genetic drift), and no migration or gene flow. Under these conditions, the allele frequencies in the population remain constant from generation to generation.

As a result, if a population is truly in Hardy-Weinberg equilibrium, the frequencies of both alleles and the genotypes that arise from those alleles do not change. This principle serves as a null hypothesis for testing evolutionary processes, as any deviation from this equilibrium suggests that one or more of the assumptions are being violated, leading to changes in allele frequencies due to factors such as natural selection, mutation, or genetic drift.

The other options reflect concepts that would lead to changes in a population's genetic structure, hence they do not align with the definition of Hardy-Weinberg equilibrium.