What is Hardy-Weinberg equilibrium?

• A. In a large and random mating population, and in the absence of selection, mutation, and migration, gene and genotypic frequencies remain constant generation to generation
• B. In a population with frequent migration, genotypic frequencies fluctuate
• C. When there is selection, allele frequencies remain unchanged
• D. When mating is assortative, allele frequencies remain constant

Answer: (A)

Hardy-Weinberg equilibrium describes a population where allele and genotype frequencies stay constant from generation to generation when there is random mating and no evolutionary forces acting. In this situation, if the two alleles have frequencies p and q (p + q = 1), the genotype frequencies are p^2 for having two copies of the first allele, 2pq for heterozygotes, and q^2 for two copies of the second allele, and these proportions remain unchanged each generation. The statement that best matches this idea is: in a population that is large and mates randomly, and in the absence of selection, mutation, and migration, gene and genotypic frequencies remain constant generation to generation. If migration occurs, allele frequencies can shift, altering the equilibrium. If there is selection, certain alleles are favored and their frequencies change over time. Nonrandom mating, such as assortative mating, disrupts random mating and changes genotype frequencies even if allele frequencies may not stay constant.