a) In a randomly mating laboratory population of Drosophila, 9% of the flies hav

Question

a) In a randomly mating laboratory population of Drosophila, 9% of the flies have black bodies (encoded by the autosomal recessive ebonygene) rather than the wild-type tan colour. What proportion of the population would you expect to be heterozygous at the ebonylocus?

b) All the black flies were removed from this population before they could mate, and the remaining tan flies allowed to mate at random. What is the frequency of the ebonyallele in these tan flies?

c) What would you expect the proportion of black-bodied flies to be in the next generation?

Explanation / Answer

a) The frequency of the recessive phenotype 0.09. Assuming H-W equilibrium, this is q2 , so q = 0.3, p= 0.7, and the frequency of heterozygotes = 2 x 0.3 x 0.7 = 0.42(or 42%, which is also acceptable).

b) The tan flies were 91% of the original population, so the proportion of tan flies that are heterozygotes is 42/91. Each of these carries one ebonyallele, so the frequency of ebonyis 21/91 = 0.2308.

c) The new q2 = (21/91)2 = 0.053

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