Suppose that an allele is present in blue-footed booby offspring that causes a nestling to share its food with its nestmate if it is not particularly hungry during times of adequate food availability. This gene imposes a fitness cost of 0.3 on those who carry it, while conferring a benefit of 0.4 on the sibling who receives the additional food. Will this gene increase in frequency if the two nestmates are always half siblings (with the same mother but different fathers)?

Question

Quizplus · Accepted Answer

The coefficient of relatedness (r) between half siblings is 0.25. The cost of carrying the allele is 0.3, which means that the reduction in fitness for the individual carrying the allele is 0.3. The benefit of the allele is 0.4, but this benefit is only realized by the half-sibling, who has a relatedness coefficient of r = 0.25. The net effect of the gene on fitness is therefore: rb F1F1F1S1F1F1F10 c = (0.25 x 0.4) - 0.3 = 0.1 - 0.3 = -0.2. Since the net effect is negative, the gene will not increase in frequency in the population.

Suppose That an Allele Is Present in Blue-Footed Booby Offspring