Question

The frequency two alleles “A” and “a” is 0.25 and 0.75, respectively.
a) Assuming H-W equilibrium, what is the expected frequency of heterozygotes in the population? What about the frequency of homozygous dominant individuals?
b) How many individuals would have each genotype in a population of 20,000?

Answer 1

Using the H-W assumptions that establish that:

p = Dominant allele

q = Recessive allele

p + q = 1

p2 = frequency of homozygous dominant

q2 = frequency of homozygous recessive

2pq = frequency of heterozygous

Frequency of heterozygotes in the population?

p = 0.25

q = 0.75

2 x p x q = 2 x 0.25 x 0.75 = 0.375

0.375

Frequency of homozygous dominant in the population?

p2 = 0.252 = 0.0625

How many individuals would have each genotype in a population of 20,000?

q2 = 0.752 = 0.56

Observing the frequencies, there are:

56% of homozygous recessive

6% of homozygous dominants

37% of heterozygous

The last thing that you need to do is to calculate how many people from your population represent these percentages

Number of heterozygous individuals = 20000 x 0.06 = 1200

Number of homozygous recessive individuals = 20000 x 0.56 = 11200

Number of homozygous dominant individuals = 20000 x 0.37 = 7400