Q22 of 30 Page 1

(a) Sickle celled anaemia in humans is a result of point mutation. Explain.

(b) Write the genotypes of both the parents who have produced a sickle celled anaemic offspring.


a) Sickle cell anaemia is a recessive autosomal disease . It is controlled by a single pair of alleles, HbA and HbS. The defect is caused by point shift mutation i.e. substitution of Glutamic acid by Valine at 6th position of the Beta -Globin chain of haemoglobin molecule.


b) To produce a sickle cell anaemic offspring both of the parent should be a carrier or one should be a carrier and other should be a carrier.


i.e. the genotype should be :


1) HbA, HbS (one parent) and HbA, HbS (other parent)


2) HbS, HbS (one parent) and HbA, HbS (other parent).


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