A population is in Hardy- Weinberg equilibrium for a gene with only two alleles. If the gene frequency of an allele A is 0.7, the genotype frequency of Aa is
(a) 0.21
(b) 0.42
(c) 0.36
(d) 0.7
(b) 0.42
Explanation:
For a gene with two alleles, A (dominant) and a (recessive), if the frequency of A is p and the frequency of a is q, then the frequencies of the three possible genotypes (AA, Aa, and aa) can be expressed by the Hardy-Weinberg
p2 + 2pq + q2 = 1
where, p2 = frequency of AA (homozygous dominant) individuals, 2pq = frequency of Aa (heterozygous) individuals and q2 = frequency of aa (homozygous recessive) individuals. The equation can be used to calculate allele frequencies if the numbers of homozygous recessive individuals in the population is known. Here, p = 0.7 and q = 0.3 (given)
∴ 2pq (frequency of heterozygote)
= 2 × 0.7 × 0.3 = 0.42