In a population of butterflies, the G gene affects color in the larval stage (ca
ID: 83236 • Letter: I
Question
In a population of butterflies, the G gene affects color in the larval stage (caterpillars). GG caterpillars are dark green, Gg caterpillars are medium green, and gg caterpillars are light green. Because the Gg caterpillars blend best with the foliage, the survival probabilities of the three genotypes are 0.05 for GG, 0.2 for Gg, and 0.02 for gg. If all individuals have equal survival after the caterpillar stage and are equally fertile, what are the relative fitnesses of the three genotypes? What will be the allele frequencies at equilibrium?
Explanation / Answer
The survival probabilities of three genotypes tested are
GG - 0.05; Gg - 0.2; gg - 0.02.
The relative fitnesses can be obtained by dividing each of the survival probabilities by the largest probability (here it is 0.2 for Gg)
Therefore, relative fitnesses are
GG - 0.05/0.2 = 0.25; Gg - 0.2/0.2 = 1; gg - 0.02/0.2 = 0.1.
The selection coefficients are s - 0.75 for GG and t = 0.9 for gg.
A gene showing heterozygote advantage will attain an equilibrium frequency of
q= s/(s+t) Therfore, q = 0.75 /(0.75+0.9)
q = 0.45
Now from equation p+q =1
p = 1-q =1-0.45 = 0.55
Thus,
relative fitnesses are GG - 0.25; Gg - 1; gg - 0.1.
and allele frequencies are p = 0.55, q = 0.45.
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