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Question: Answered & Verified by Expert
In sickle-cell anaemia, the defect is caused by the substitution of ____(i)____ by ____(ii)_____ in the ___(iii)___ position of the beta-globin chain of the haemoglobin molecule.
BiologyPrinciples of Inheritance and VariationNEET
Options:
  • A (i) Val, (ii) Glu, (iii) nineth
  • B (i) Glu, (ii) Val, (iii) sixth
  • C (i) Val, (ii) Ser, (iii) fifth
  • D (i) Gly, (ii) Val, (iii) seventh
Solution:
2482 Upvotes Verified Answer
The correct answer is: (i) Glu, (ii) Val, (iii) sixth
The defect in sickle-cell anaemia 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. 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.

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