Chapter 21, Problem 26P

You have identified an autosomal gene that contributes to tail size in male guppies, with a dominant allele B for large tails and a recessive allele b for small tails. Female guppies of all genotypes have similar tail sizes. You know that female guppies usually mate with males with the largest tails, but the effects of population density and the ratio of the sexes on this preference have not been studied. You therefore place an equal number of males in three tanks. In tank 1, the number of females is twice the number of males. In tank 2, the numbers of males and females are equal. In tank 3, half as many females as males are present. After mating, you find the following proportions of small-tailed males among the progeny: tank 1, 16%; tank 2, 25%; tank 3, 30%.

a.	In your original population (before the animals were placed in the three tanks), 25% of the males have small tails. Assuming that the allele frequencies in males and females are the same, calculate the frequencies of B and b in your original population.
b.	Calculate Δq for each tank.
c.	If WBB = 1.0, what is WBb for each tank?
d.	If WBB = 1.0, is Wbb less than, equal to, or greater than 1.0 for each tank?