Under what circumstances would a population be expected to be in Hardy-Weinberg equilibrium?

Under what circumstances would a population be expected to be in Hardy-Weinberg equilibrium?

• A. Very large population, random mating, no mutation, no migration, no natural selection, and no genetic drift.
• B. Very small population with strong selection.
• C. Nonrandom mating and migration.
• D. Mutation pressure present.

Answer: (A)

Hardy-Weinberg equilibrium describes a population that is not evolving, so allele and genotype frequencies stay constant from generation to generation. The key is that none of the forces that drive evolution are acting: there is no mutation introducing new alleles, no migration bringing in or out alleles, no natural selection favoring some genotypes, no genetic drift from small population size, and mating is random. When these conditions hold, allele frequencies p and q remain the same and the genotype frequencies stabilize in the proportions p^2, 2pq, and q^2 after random mating. If any of those conditions are violated—such as a very small population causing drift, nonrandom mating, migration, mutation, or selection—the population will evolve and will no longer fit Hardy-Weinberg expectations. The scenario described, with a very large population and random mating and no mutation, migration, selection, or drift, is precisely when Hardy-Weinberg equilibrium would be expected.

Hardy-Weinberg equilibrium describes a population that is not evolving, so allele and genotype frequencies stay constant from generation to generation. The key is that none of the forces that drive evolution are acting: there is no mutation introducing new alleles, no migration bringing in or out alleles, no natural selection favoring some genotypes, no genetic drift from small population size, and mating is random. When these conditions hold, allele frequencies p and q remain the same and the genotype frequencies stabilize in the proportions p^2, 2pq, and q^2 after random mating. If any of those conditions are violated—such as a very small population causing drift, nonrandom mating, migration, mutation, or selection—the population will evolve and will no longer fit Hardy-Weinberg expectations. The scenario described, with a very large population and random mating and no mutation, migration, selection, or drift, is precisely when Hardy-Weinberg equilibrium would be expected.