Sickle cell anaemia occurs due to a mutation that changes a codon on mRNA from

The mutation involving a single base substitution at the sixth codon of the beta globin gene from GAG to GUG causes the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the haemoglobin molecule. 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.