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Sickle-cell anaemia is caused by:
ATrisomy of chromosome 21
BA single base substitution at the 6th codon of β-globin gene (GAG → GUG), causing Glu → Val replacement
CChromosomal deletion of a whole gene
DX-linked recessive mutation
Answer & Solution
Correct answer: B. A single base substitution at the 6th codon of β-globin gene (GAG → GUG), causing Glu → Val replacement
**Sickle-cell anaemia** = **point mutation** (single base substitution): GAG → GUG at codon 6 of the β-globin gene → Glu replaced by Val. The mutant haemoglobin (HbS) polymerises at low O₂, deforming the RBC from biconcave to sickle shape. Autosomal recessive.
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