A population of insects is subject to predation by bats. Bats prey upon 20% of w

Question

A population of insects is subject to predation by bats. Bats prey upon 20% of white insects every generation and each surviving insect produces 6 offspring per generation. The initial population size is 100 and the initial genetic composition is :

Genotype   BB    BW     WW

Phenotype Black Black White

                    B       W

Initial allele frequencies 0.4   0.6

a) Calculate the initital genotype frequnecies after selection. Then, calculate the allele and genotype frequncies in the next two generations after selection. Show all details of your calculations

b) After 50 generations, both alleles are still present in the population. Explain why one of the alleles did not disappear by then despite the predation selection.

c) Determine the expected numbers of individuals from each phenotype after 2 generations if the population were to behave according to the Hardy Weinburg Equilibrium Model. Then test whether the population under selection is in Hardy Weinberg Equilibrium after 2 generations. Show all your calculations.

Explanation / Answer

a). BB genotype frequency is 0.16 (B2=0.4x0.4)

WW genotype frequency is 0.36 (W2=0.6x0.6)

2BW genotype frequency= 2 x 0.24=0.48 (2BW= 2 x 0.4 x 0.6)

In the first generation, BB x WW

4BW results in (4 x 0.25) so that frequency would be 1 and each allelic frequency would be 0.5

In the 2nd generation BW x BW,

BB (1): BW (2): WW (1), so allelic frequency would be 0.16, 0.48 and 0.36 respectively.

b). They might be independent variables and only 20% pray does not affect the disappearance of 'W' allele from the gene pool since, one survival white insect could produce the 6 offsprings.

c). It behaves under the Hardy Weinburg Equilibrium. The white genotype (WW) population is 36 out of 100 at the initial state and other genotypes are black (BB)-16 and BW (48). In that, 20% means ~7 will be eaten by the bats so that rest are 29 (survived). If each insect produces 6 offsprings that would be about 174 (WW) total in first generation. In 2nd generation again 20% will be disappeared by pray, so that, the total white (WW) insects would be ~139.

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