Question

In sickle cell anaemia, which of the sequences get changed?

• A. $\alpha$-chain
• B. $\beta$-chain
• C. Both A and B
• D. None of the above

Answer 1

Answer: (B)

$\beta$-chain

Hemoglobin has four protein subunits, two $\alpha$-globin and two $\beta$-globin. The Hbb gene codes the beta chain. Missense mutation, replacement of A by T at the 17${}^{th}$ nucleotide of the Hbb gene changes the codon GAG (glutamic acid) to GTG (which encodes valine).

The mutated alllele Hb${}^s$ encodes the abnormal hemoglobin molecules which stick to one another and cause stiffness and sickle shape of red blood cells. Function of hemoglobin is to transport oxygen from the lungs to other parts of the body. The sickle shaped RBC block and damage the vital organs and tissue. The hemoglobin $\beta$-gene is located on chromosome 11.