Industrial melanism refers to the dark pigmentation that evolved in some insects
ID: 31906 • 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
So you'll need to use the Hardy-Weinberg equation to solve this. However, you are told the proportion of the population which exhibits the dominant phenotype. In the H-W equation:
p^2 + 2pq + q^2 = 1
Both p^2 and 2pq represent the proportions of the population exhibiting the dominant phenotype.
However, if you know that 79% of the population shows the dominant phenotype, you know that 21% of the population exhibits the recessive phenotype (q^2 in the H-W equation).
So, q^2 = 0.21
q = 0.45
Since p+q = 1,
p = 1 - q = 0.55
(p is the frequency of the dominant allele in the population.)
The proportion of heterozygotes will be 2pq = 2 (0.55)(0.45) = 0.49. So, 49% of the population is heterozygous for this trait.