question_answer

Directions : (31 - 35)

Read the passage given below and answer the following questions.

Sickle cell anaemia is an autosome (chromosome 11) linked recessive trait that can be transmitted from parents to the offspring when both the partners are carrier for the gene or heterozygous. The disease is controlled by a single pair of allele, \[H{{b}^{A}}\] and \[H{{b}^{S}}\]. Out of .the three possible genotypes only homozygous individuals i.e., \[H{{b}^{S}}H{{b}^{S}}\] show the diseased phenotype. Heterozygous \[\left( H{{b}^{A}}H{{b}^{S}} \right)\] individuals appear apparently unaffected or normal but they are carrier of the disease as there is 50 per cent probability of transmission of the mutant gene to the progeny, thus exhibiting sickle-cell trait. The defect is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the haemoglobin molecule. The substitution of amino acid in the globin protein results due to the single base substitution at the sixth codon of the beta globin gene from GAG to GUG. The mutant haemoglobin molecule undergoes polymerization under low oxygen tension causing the change in the shape of the RBC from biconcave disc to elongated sickle like structure.

Sickle cell anaemia is :

A) Autosomal dominant inheritance

B) X-linked recessive inheritance

C) Autosomal recessive inheritance

D) X-linked dominant inheritance