A dominant-acting allele (B) in cardinals makes males susceptible to parasites t

Question

A dominant-acting allele (B) in cardinals makes males susceptible to parasites that cause the birds to lose all their head feathers. Female cardinals prefer to mate with non-bald males, so that the relative fitness of non-bald males is 1.0 while that of bald males is 0.75. A. (1 pt) What model of selection is acting at this locus? B. (1 pt) What is the relative fitness of heterozygous (Bb) males? C. (1 pt) What is the strength of selection (s) against the bald males? D. (1 pt) A population has allele frequencies fB)-0.5 and ftb) -0.5. What is the average fitness of this population?

Explanation / Answer

A. Here, the non-bald males (recessive) have higher relative fitness than that of the bald males (dominant). As the recessive allele is preferred, the mode of selection in this case is 'Selection against the dominant alllele'

B. For Selection against the dominant alllele, the relative fitness of heterozygous (w12) is same as the relative fitness of dominant homozygous (w11). Here relative fitness of dominant homozygous is 0.75. So relative fitness of heterozygous is also 0.75.

C. w11 = w12 = 1-s = 0.75

=> s = 1-0.75 = 0.25

s = 0.25

D. Given:

p = 0.5; q = 0.5; w11 = 0.75; w12 = 0.75 (from B); w22 = 1

Solution:

p2 = 0.52 = 0.25

2pq = 2*0.5*0.5 = 0.5

q2 = 0.52 = 0.25

Average fitness (w) = p2w11 + 2pqw12 + q2w22 = (0.25*0.75) + (0.5*0.75) + (0.25*1) = 0.1875+0.375+0.25 = 0.8125

Average fitness (w) =0.8125

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