<prompt> The primary defect which leads to sickle cell anemia isAn abnormality in porphyrin part of hemoglobinReplacement of glutamate by valine in βchain of HbAA nonsence mutation in the β chain of HbASubstitution of valine by glutamate in the achain of HbA  <response>: Sickle cell anemia Sickle cell anemia is a hereditary hemoglobinopathy, i.e. the type of disease characterized by the production of defective hemoglobin.Normal hemoglobinThe hemoglobin molecule is an assembly of four globular protein.Each subunit is composed of a protein part, i.e, globin and a nonprotein part, i.e. heme, i.e. Each hemoglobin molecule contain four heme units and two pairs of a similar protein, globin.The heme part of the globular protein is same in all types of hemoglobin.The protein part vary in different hemoglobin -Adult hemoglobin Hemoglobin A consists of two identical α-chains and two identical δ-chains.Fetal hemoglobin HbF consists of two identical a-chains and two identical γ chains.Minor hemoglobin HbA, consists of two identical a-chains and two identical δ chains.Normally adult blood contains about 96 of HbA α2 β2 3-3.5 HbA2α2 δ2, and small amount of fetal hemoglobin HbF α2 γ2.Defect in sickle cell anemia Sickle cell anemia results from a mutation in β-globin gene.It is caused by a point mutation at the sixth position of the β-globin chain leading to a substation of a valine residue for a glutamic acid residue. resulting in sickle hemoglobin HbS.Sickle cell anemia is an autosomal recessive disorder.If an individual is homozygous for the sickle cell mutation, almost all the hemoglobin in the red cell is HbS.In heterozygotes, only about 40 of the hemoglobin is HbS, the remainder being normal hemoglobins. 