Question

Assertion :Only a boy child could be born with a substitution of glutamic acid by valine on $6$th codon of $\beta$-chain of haemoglobin. Reason: The gene for above mutation occurs on Y-chromosome.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is D Both Assertion and Reason are incorrect

Sickle cell anaemia is an autosomal recessive hereditary disorder in which the erythrocytes become sickle-shaped under oxygen deficiency as during strenuous exercise and at high altitudes. The disorder or disease is caused by the formation of abnormal hemoglobin called haemoglobin-S. As found out by Ingram (1958), haemoglobin-S differs from normal haemoglobin- A in only one amino acid-6th amino acid of β-chain, glutamic acid, is replaced by valine due to substitution (transversion) of T by A in the second position of the triplet codon (CTC) which is changed to CAC in the B-haemoglobin gene situated on chromosome 11.

So, the correct answer is 'Both Assertion and Reason are incorrect'.