In Hardy-Weinberg equilibrium, what happens to genotype frequencies across generations if allele frequencies remain constant?

• A. They remain constant across generations
• B. They oscillate across generations
• C. They increase in frequency
• D. They decrease in frequency

Answer: (A)

In Hardy-Weinberg equilibrium, once the allele frequencies p and q are fixed, the genotype frequencies are determined by those same constants: p^2 for the homozygote of one allele, 2pq for the heterozygote, and q^2 for the homozygote of the other allele. If p and q do not change from one generation to the next, the genotype proportions derived from them do not change either. Therefore the genotypes remain the same across generations.

Oscillating would require allele frequencies to change each generation. Increasing or decreasing would require forces like selection, drift, migration, or mutation acting to alter p and q. Since those forces are assumed absent here, the genotype frequencies stay constant.