<prompt> Sickle cell anemia is due to:AdditionDeletionNonePoint mutation  <response>: Sickle 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 valineresidue for a glutamic acid residue. In homozygous state -100 chains defective i.e., no HbA In heterozygousstate -40 chains defective i.e., HbA present HbA α2β2 Hb A2 α2δ2 HbF α2γ2 Most important factorwhich affects degree of sickling is amount of Hb S and its interaction with other Hb chains Factors favouring polymerization Hypoxia -2,3 BPG polymerization Acidosis - acidosis polymerization Hb concentration -1 Hb concentration polymerization Combination with other hemoglobins - already discussed 