Sickle cell anaemia is caused by a mutation in the hemoglobin-beta gene found on chromosome 11. The defect is caused by the substitution of glutamic acid (Glu) by valine (Val) at the sixth position of the beta-globin chain of the haemoglobin molecule. The substitution of amino acid in the globin protein results due to the single base substitution at the sixth codon of the beta-globin gene from GAG to GUG.