Question

If at a locus, three alleles in a population, such that the A allele is present at frequency 0.2, and C allele at frequency 0.4, after one generation of random mating in a population of size 100, the total number of A/A homozygotes will be:

Select one:

a. 3

b. 64

c. 4

d. 12

e. 24

Answer 1

Answer : (c) 4

There are 3 alleles in the population - A, B and C

According to Hardy-weinberg equilibrium, p + q + r = 1, where

Frequency of allele A (p) = 0.2

Frequency of allele C (r) = 0.4

Then, Frequency of allele B (q) = 1 - (0.2 + 0.4) = 0.4

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After one generation, according to Hardy-weinberg equilibrium,

p2 + q2 + r2 + 2pq + 2pr + 2qr = 1

Where,

p2 = frequency of homozygotes A/A

q2 = frequency of homozygotes B/B

r2 = frequency of homozygotes C/C

2pq = frequency of heterozygotes A/B

2pr = frequency of heterozygotes A/C

2qr =frequency of heterozygotes B/C

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So, the frequency of homozygotes A/A is p2 = 0.2 x 0.2 = 0.04

There are total 100 individuals in the population.

So, the the total number of A/A homozygotes = 0.04 x 100 = 4