A gene locus has two alleles A, a. If the frequency of dominant allele A is 0.4, then what will be the frequency of homozygous dominant, heterozygous and homozygous recessive individuals in the population?

Solution & Explanation

Answer: (C) 0.16(AA); 0.48(Aa); 0.36(aa). Using the Hardy-Weinberg principle, if the dominant allele A has frequency p = 0.4, then the recessive allele a has frequency q = 1 - 0.4 = 0.6. Homozygous dominant (AA) = p² = 0.16, heterozygous (Aa) = 2pq = 2 × 0.4 × 0.6 = 0.48, and homozygous recessive (aa) = q² = 0.36. NCERT Reference: Ch 6 Evolution, p.121, lines 4–9: "The frequency of AA individuals in a population is simply p2. This is simply stated in another ways, i.e., the probability that an allele A with a frequency of p appear on both the chromosomes of a diploid individual is simply the product of the probabilities, i.e., p2. Similarly of aa is q2, of Aa 2pq."