question_answer

The sickle cell (s) allele has a relatively high frequency \[(0.12)\] in central Africa, even though individuals homozygous for this allele usually die before they reach the reproductive age. Which of the following statements are correct for Sickle cell anaemia?

I. The defect is caused by the substitution of glutamic acid by valine at sixth position of the beta chain of the haemoglobin.

II. IIeterozygotes \[(H{{b}^{A}}H{{b}^{s}})\] individuals appear apparently unaffected and enjoy some resistance to malaria.

III. The mutant haemoglobin molecule undergoes polymerization under low oxygen tension causing the change in the shape of the RBC.

IV Female homozygous for this allele are more fertile than those who lack it.

A)  I and II                       

B)  I, II and IV

C)  I, III and IV                 

D)  II, I and III