a. What is the frequency of the a allele? b. What is the frequency of the heterozygous genotype? c. What is the frequency of the homozygous dominant genotype?

Question

A population of butterflies exhibits two phenotypes for antennae - - club shaped are dominant over curly, represented by the alleles A and a. In a population of 1000 butterflies, 250 have curly antenna.

Answer 1

Allele for club shaped = A

Allele for curly shape = a

Club shaped is dominant over curly shape, so A is dominant over a

Frequency of homozygous curly butterflies (aa butterflies) = 250 curly antenna butterfly / 1000 total butterfly = 0.25 = 25%.

Frequency of the a allele = sqrt (0.25) = 0.5 or 50%.

The frequency of the recessive allele is also referred to as q.

In this case, q = 0.5.

Frequency of A allele = 1-(frequency of a allele) = 1-0.5 = 0.5 or 50%.

The frequency of the dominant allele is also referred to as p.

In this case, p = 0.5.

Frequency of heterozygous genotype = freq of Aa + freq of aA = (0.5*0.5) + (0.5*0.5) = 0.25 + 0.25 = 0.5 or 50%

freq of Aa is the probably of the mother contributing an A allele and the father contribute an a allele.

freq of aA is the probably of the mother contributing an a allele and the father contribute an A allele.

Overall, the probability of the Aa genotype = 2pq = 2*0.5*0.5 = 0.5 or 50%

Frequency of the homozygous dominant genotype = freq AA = 0.5*0.5 = 0.25 or 25%.

Alternatively, you can say the freq of AA = p² = 0.5² = 0.25 or 25%