Question

Cystic fibrosis is an autosomal recessive condition. The frequency of cystic fibrosis is 0.000484, or about 1 in 2000 people. What is the frequency of the allele for cystic fibrosis? What percent of people are carriers (heterozygous) for cystic fibrosis?

Answer 1

Answer: Allele frequency for cystic fibrosis is 0.022.

4.302% carriers (heterozygous) for cystic fibrosis in the population.

Explanation: Using F to represent the allele, homozygosity (ff) produces a disorder in autosomal recessive disorders. Therefore, the allele representation goes thus;

Cystic fibrosis (Homozygous) = ff = q²

Normal (Homozygous) = FF = p²

Carrier (Heterozygous) = Ff = 2pq

Frequency of cystic fibrosis q² is given as 0.000484

Therefore, allele frequency of cystic fibrosis, q = √0.000484 = 0.022

Recall that p+q = 1

Therefore, allele frequency for normal individual,

p = 1 - q = 1 - 0.022 = 0.978

Also, carrier (heterozygous) frequency, 2pq = 2 x 0.978 x 0.022 = 0.043032

Hence, Percentage of people who are carrier for cystic fibrosis in the population will be

0.043032 x 100 = 4.302%