There is a population of Drosophila flies in a small fruit shop

Due to sudden mutation, the eye color of some of the flies changes from red to white

Red (represented by R) is the dominant gene, and white (represented by r) is a recessive gene

Due to this, the gene frequency of allele r changes from 0.38 to 0.40.

What will be the new genotype frequencies in that population?

(p + q = 1, p2 + 2pq + q2 = 1)

A.) p2 = 0.36, 2pq = 0.48, q2 = 0.16

B.) p2 = 0.32, 2pq = 0.23, q2 = 0.45

C.) p2 = 0.25, 2pq = 0.36, q2 = 0.39

The answer is A. p2 = 0.36, 2pq = 0.48, q2 = 0.16.

Let's first distinguish alleles frequencies from genotypes frequencies:

p - a frequency of R allele,

q - a frequency of r allele,

p² - a frequency of RR genotype,

2pq - a frequency of Rr genotype,

q² - a frequency of rr genotype.

The gene frequency of allele r changes from 0.38 to 0.40, thus:

q = 0.40

Now, we will implement this in the following equation:

p + q = 1

If q = 0.40, then:

p + 0.40 = 1

⇒ p = 1 - 0.40

⇒ p = 0.60

Now, the frequencies of both alleles are know and it is easy to calculate the genotype frequencies:

- the frequency of RR genotype: p² = 0.60² = 0.36

- the frequency of Rr genotype: 2pq = 2 · 0.60 · 0.40 = 0.48

- the frequency of rr genotype: q² = 0.40² = 0.16

Therefore, the new genotype frequencies in that population are p2 = 0.36, 2pq = 0.48, q2 = 0.16.