Question

Sickle cell anaemia is an example of:

• A. Sex-linked dominant disease
• B. Sex-linked recessive disease
• C. Autosomal dominant disease
• D. Autosomal recessive disease

Answer 1

The correct option is D

Autosomal recessive disease

This is an autosome linked recessive trait that can be transmitted from parents to the offspring when both the partners are carriers for the gene (or heterozygous). The disease is controlled by a single pair of allele- $H{b}^S$. Out of the three possible genotypes only homozygous individuals for $H{b}^S\left(H{b}^{S}H{b}^S\right)$ show the diseased phenotype. Heterozygous $\left(H{b}^{A}H{b}^S\right)$ individuals appear apparently unaffected but they are a carrier of the disease as there is 50 per cent probability of transmission of the mutant gene to the progeny.