Sickle cell anaemia is due to:

Ans: c (Point mutation) Ref: Robbins, 7th ed,p. 628Sickle cell disease is a hereditary hemoglobinopathy, characterized by the defective haemoglobins.It is caused by a point mutation at the sixth position of the beta globin chain leading to substitution of valine residue for a glutamic acid residue.In homozygous state -100 % chains defective i.e., no HbAIn heterozygous state -40 % chains defective i.e., HbA presentHbA = a2b2 Hb A2 = a2d2HbF = a2g2* Most important factor which affects degree of sickling is amount of Hb S and its interaction with other Hb chainsFactors favouring polymerization# Hypoxia -|2,3 BPG - | polymerization# Acidosis - | acidosis - | polymerization# Hb concentration -1 Hb concentration -| polymerization# Combination with other hemoglobins - already discussed