An autosome linked recessive trait, transmitted from parents to the offspring when both the partners are carrier for the gene (or heterozygous).
Controlled by a single pair of allele, HbA and HbS.
Only homozygous individuals for HbS (HbSHbS) show the diseased phenotype.
Heterozygous (HbAHbS) individuals are unaffected but they are carrier of the disease as there is 50 per cent probability of transmission of the mutant gene to the progeny.
Substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the haemoglobin molecule due to the single base substitution at the sixth codon of the beta globin gene from GAG to GUG.
The mutant haemoglobin molecule undergoes polymerisation under low oxygen tension causing the change in the shape of the RBC from biconcave disc to elongated sickle like structure