Question

The most striking example of frameshift mutation was found in a disease called as

• A. Sickle cell anaemia
• B. Colour blindness
• C. Leshc-Nyhan Syndrome
• D. Thalassemia

Answer 1

The correct option is D Thalassemia

Haemoglobin has four protein subunits, two $\alpha$-globin and two beta-globin. The Hb${}^b$ gene codes the $\beta$-chain. A missense mutation, replacement of A by T at the 17th nucleotide of the Hbb gene changes the codon GAG (glutamic acid) to GTG (which encodes valine). Thus, the disease is caused by the point mutation (change in single nucleotide base) in the gene. Colour blindness is X-linked recessive disorder which is caused by the point mutation in genes that code for red and green light-sensitive proteins leads to faulty cone cells which are responsible for colour perception. Lesch-Nyhan syndrome is caused by the single point mutation in HPRT gene present on X-chromosome which in turn leads to an absence of low levels of hypoxanthine guanine phosphoribosyltransferase 1 (HPRT), an enzyme for purines recycling. Thalassemia is a group of blood disorders which are caused by mutations in the HbB and HbA genes present on chromosome 11 and chromosome 16 respectively. The unequal crossover within globin gene complexes causes deletion which in turn leads to backwards shifting of the reading frame. The correct answer is D.