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In sickle-cell anaemia, what is the expected ratio of normal : carrier : sickle-cell anaemic children from a marriage between **two carriers** (Hb^A Hb^s × Hb^A Hb^s)?
A1 : 1 : 1
B3 : 0 : 1
C1 : 2 : 1
D9 : 3 : 4
Answer & Solution
Correct answer: C. 1 : 2 : 1
Standard Mendelian monohybrid cross of two heterozygotes: 1 Hb^A Hb^A : 2 Hb^A Hb^s : 1 Hb^s Hb^s — i.e. 1 normal : 2 carriers : 1 sickle-cell anaemic. (Because homozygous Hb^s Hb^s individuals often die early, the surviving ratio is approximately 1 normal : 2 carriers, reflecting the pleiotropic + lethal aspect.)
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