Question

You identify a population of rats on an island. Their coat color is controlled by a single gene: BB rats are black, Bb rats are gray, and bb rats are white. You take a census of the population and record the following numbers of rats

Black 150

Gray 120

White 30

a) What are the frequencies of the two alleles?

b) What are the Hardy-Weinberg equilibrium frequencies for these three phenotypes?

c) A heat wave hits the island. All 150 rats with black fur die from heat stroke, but the other rats survive. What are the new allele frequencies for the population?

d) If the population suffers no further cataclysms after the heat wave, and the surviving animals mate randomly, what will be the frequency of rats with black fur in the next generation?

Answer 1

According to question :

BB = 150
Bb = 120
bb = 30

a) According to Hardy-Weinberg equilibrium, let B = p and b= q

Frequency of B allele = 150 / 300 = 0.5
Frequency of b allele = 30 / 300 = 0.1

b) Hardy Weinberg frequencies are :

B = [ (2 x 150) + 120 ] / 600 = 0.7

b = [ (2 x 30) + 120 ] / 600 = 0.3

c) If only the gray and white rats survived, the new allele frequencies are :

B = 120 / 300 = 0.4

b = [ (2 x 30) + 120 ] / 300 = 0.6

d) So now Bb will mate with bb . This will produce : Bb, Bb, bb and bb

There will be no black coat colored rats in the next generation. The coat colors will be gray and white only. So frequency of black coat colored rats will be zero.