Sickle Cell Mutation and Polymerization — NEET Biology
✅ Asked in NEET 2026The sixth mutant codon of beta globin gene causing polymerization of haemoglobin and change in RBC shape is
The sixth mutant codon of beta globin gene causing polymerization of haemoglobin and change in RBC shape is
Answer & NCERT explanation
Correct answer: A — GUG
Sickle-cell anaemia results from a single nucleotide change at codon 6 of the beta-globin gene from GAG (Glu) to GUG (Val). The Val substitution allows HbS to polymerise and distorts the RBC shape.
Read more NCERT concept on the PYQ
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. 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.
NTA tests understanding of how a single base substitution (GAG → GUG) in the beta-globin gene causes glutamic acid to be replaced by valine, leading to abnormal hemoglobin polymerization under low oxygen. Students often confuse which amino acid is replaced or forget that polymerization occurs specifically under low oxygen tension, not always. The key to remember: one point mutation → one wrong amino acid → protein shape changes → cell deformation into sickle shape → hemolysis and pain. This concept appears because it perfectly illustrates gene-phenotype connection and is clinically relevant for NEET's genetics focus.
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