Question

An individual heterozygous for cystic fibrosis

a) Will have children who are all carriers of cystic fibrosis.

b) Cannot have children with cystic fibrosis.

c) has cystic fibrosis

d) is a carrier

Answer 1

The answer is option (d)

Cystic fibrosis is a recessive disease. A person must have mutation in both copies of the gene to have the disease. An individual heterozygous for the cystic fibrosis mutation will have one copy of the mutated gene and one copy of the normal gene. Hence that individual is a carrier of cystic fibrosis and does not show any symptoms. If this individual marries a person homozygous for the mutated gene, then all the children will be either carrier or will have cystic fibrosis. However, if the individual marries a person homologous for normal gene, then there is three in four (75%) chance that the child will not carry the mutated gene and hence not be a carrier of the disease.