Question

The condition of sickle cell anaemia is due to

• A. Chromosomal mutation
• B. Silent mutation
• C. Point mutation
• D. Frameshift mutation

Answer 1

Answer: (C)

Point mutation

Sickle cell anaemia is caused by a mutation in Hb${}^b$ gene, that codes the $\beta$-chain, causing replacement of A by T at the 17th nucleotide of the Hb${}^b$ gene changes the codon GAG (glutamic acid) to GTG (which encodes valine). Mutation in single nucleotide base of a DNA segment is called as a point mutation. It can introduce a premature stop codon, or a nonsense codon in the transcribed mRNA (nonsense mutation) or changes a codon specifying a different amino acid (missense mutation). Thus, the mutation in Hb${}^b$ gene is a point mutation causing a change in a codon specifying a different amino acid. The correct answer is C.