Question

Cystic fibrosis is an autosomal recessive disease. In an island having a population of 200 people, 98 people suffer from cystic fibrosis. How many people are carriers of this disease?

• A. 42
• B. 84
• C. 18
• D. 64

Answer 1

Answer: (B)

Cystic fibrosis is caused due to a recessive gene. Individuals suffering from this disease are homozygous recessive. Applying Hardy Weinberg's equation here, $q^2=\frac{98}{200}=0.49$ . Hence, $q=0.7$ . Thus $p=1-q=\mathrm{0.3.}$
If the carrier of this disease is heterozygous individuals. Their proportion will be $2pq=2\times 0.7\times 0.3=0.42$ . In this population, carriers will be $0.42\times 200=84.$