In Hardy-Weinberg equilibrium, what conditions must be met to keep allele frequencies constant?

• A. Very large population size, random mating, no mutation, no migration, and no natural selection
• B. Small population size, nonrandom mating, mutation, migration
• C. Random mating with mutation and migration allowed
• D. Any population size with natural selection present

Answer: (A)

In Hardy-Weinberg equilibrium, allele frequencies stay constant from generation to generation when no evolutionary forces act on the population. The conditions described—an extremely large population, random mating, no mutation, no migration, and no natural selection—together ensure this. A very large population minimizes genetic drift, random mating ensures allele combinations reflect those frequencies rather than preferred pairings, and the absence of mutation, migration, and differential survival or reproduction means no new alleles are introduced or removed and no genotypes have a reproductive advantage. Under these circumstances, allele frequencies (p and q) remain constant, and genotype frequencies can be predicted by p^2, 2pq, and q^2. If any of these factors are present, allele frequencies can change over time, which is why the other scenarios fail to maintain constancy.