Principle of Inheritance and VariationMediumBloom L3
Question
Sickle cell anaemia is:
Options
A.caused by substitution of valine by glutamic acid in the beta globin chain of haemoglobin
B.caused by a change in a single base pair of DNA
C.characterized by elongated sickle like RBCs with a nucleus
D.an autosomal linked dominant trait
Solution
Sol.(b) [Key Concept: Sickle Cell Anaemia — Point Mutation] Sickle cell anaemia is caused by a CHANGE IN A SINGLE BASE PAIR OF DNA — a point mutation in the beta-globin gene. The codon GAG (glutamic acid) is mutated to GUG (valine), changing one amino acid at position 6 of the beta-globin chain. Option (a) is REVERSED (glutamic acid is replaced BY valine, not valine by glutamic acid). Option (c) is wrong — sickle RBCs have no nucleus (enucleated). Option (d) is wrong — it is autosomal RECESSIVE.
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