1. Why the RBC attains sickle …

In normal conditions, RBCs are Biconcave disc- like. Sickle cell anemia is a group of disorders which comes under the sickle cell disease. It is an autosomal recessive disease therefore it can be transmitted from parents of the offspring when both female and male individuals are carriers for the gene. The disease is controlled by a single pair of alleles, Hb^A and Hb^S. Thus, three genotypes are possible in this situation:
- Hb^A Hb^A (normal homozygous) - Hb^A Hb^S (normal carrier) - Hb^A Hb^S Hb^S (diseased, die before attaining maturity)
Heterozygous (Hb^A Hb^S) individuals appear unaffected but they are carriers of the disease as there is a 50% probability of transmission of the mutant gene to the progeny, thus exhibiting sickle cell trait.
The disease or defect is caused by a mutation (transversion) of the gene controlling the β-chain of hemoglobin. It replaces glutamic acid (Glu) present at the 6^th position of the β-chain by amino acid Valine (Val) . The mutant hemoglobin molecules undergo polymerization under low oxygen tension causing the change in the shape of RBCs from biconcave to elongated sickle- like (curve) structure.