In Hardy-Weinberg contexts, what do p^2, 2pq, and q^2 represent?

In Hardy-Weinberg contexts, what do p^2, 2pq, and q^2 represent?

• A. Genotype frequencies for AA, Aa, aa
• B. Allele frequencies for A and a
• C. Haplotype frequencies for two genes
• D. Phenotype frequencies

Answer: (A)

In Hardy-Weinberg contexts, p and q are the frequencies of the two alleles, A and a, with p + q = 1. When mating is random and conditions are met, the genotypes in the population appear in proportions p^2, 2pq, and q^2. Those numbers specifically describe how common each genotype is: p^2 is the frequency of individuals with the AA genotype, 2pq is the frequency of heterozygotes Aa, and q^2 is the frequency of the aa genotype. For example, if p = 0.7 and q = 0.3, you’d expect 0.49 of the population to be AA, 0.42 to be Aa, and 0.09 to be aa. These are genotype frequencies, not allele frequencies (which would be p and q). They aren’t haplotype frequencies (which involve combinations of alleles at different loci) and they aren’t phenotype frequencies (which depend on how genotypes are expressed).

In Hardy-Weinberg contexts, p and q are the frequencies of the two alleles, A and a, with p + q = 1. When mating is random and conditions are met, the genotypes in the population appear in proportions p^2, 2pq, and q^2. Those numbers specifically describe how common each genotype is: p^2 is the frequency of individuals with the AA genotype, 2pq is the frequency of heterozygotes Aa, and q^2 is the frequency of the aa genotype. For example, if p = 0.7 and q = 0.3, you’d expect 0.49 of the population to be AA, 0.42 to be Aa, and 0.09 to be aa.

These are genotype frequencies, not allele frequencies (which would be p and q). They aren’t haplotype frequencies (which involve combinations of alleles at different loci) and they aren’t phenotype frequencies (which depend on how genotypes are expressed).