Industrial melanism refers to the dark pigmentation that evolved in some insects
ID: 31907 • Letter: I
Question
Industrial melanism refers to the dark pigmentation that evolved in some insects giving them protective coloration on vegetation darkened by soot in heavily industrialized areas prior to air pollution regulation. Assume that in one heavily polluted area near Birmingham, England in 1956, 79% of the moths of the species Biston betularia were black due to the presence of a dominant gene for melanism. Estimate the frequency of the dominant allele in this population, and the proportion of black moths that are heterozygous.
Explanation / Answer
The frequency of alleles can be calculated using Hardy-Weinberg equation:
P2+q2+2pq = 1,
Where p is the dominant allele, p2 is the homozygous dominant genotype
q is the recessive allele ( for a bi allelic locus), q2 is homozygous recessive genotype; and
2pq is heterozygous genotype
As per the data given, 79% of the moths show dominant phenotype. The data implies that the frequency of both homozygous and heterozygous dominant alleles is 0.79 and the frequency of homozygous recessive alleles is 0.21 (21%).
Therefore, the frequency of dominant alleles is 0.79
The frequency of heterozygous population is calculated as 2 (0.79) (0.21) = 0.33
Therefore, the frequency of heterozygous population is 33%