Question

A population has 36% recessive homozygotes, for example nontasters in our class exercise. The frequency of the homozygous dominant genotype under conditions of genetic equilibrium should be what (hint-first determine allele frequencies; then determine the frequency of genotypes)?

Answer 1

Answer: frequency of the homozygous dominant genotype: 16% (0.16)

Explanation: Following are the basic genetic equilibrium formula:

1.) p + q = 1

where,

• p = frequency of dominant allele in the sample population
• q = frequency of recessive allele in the sample population

2.) p2 + 2pq + q2 = 1

where

• p2 = percentage of homozygous dominant genotype
• q2 = percentage of homozygous recessive genotype
• 2pq = percentage of heterozygous genotype

Let say A is dominant allele and a is recessive allele.

p2 = AA
q2 = aa
2pq = Aa

p = dominant allele (A)

q = recessive allele (a)

frequency of the recessive genotype (aa) is provided: 36% = 36/100 = 0.36

• q2 (q^2) = 0.36
• q = 0.6

Using formula 1,

• p + q = 1
• p = 1 - 0.6 = 0.4 (40%)

Now, from the above data the frequency of homozygous dominant genotype(AA) would be,

• p2 (p^2) = 0.4 x 0.4 = 0.16 (16%)