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A monohybrid cross between two heterozygotes (Tt × Tt) gives a phenotypic ratio of
A1 : 1
B9 : 3 : 3 : 1
C1 : 2 : 1
D3 : 1
Answer & Solution
Correct answer: D. 3 : 1
1. Cross Tt × Tt: offspring are 1 TT : 2 Tt : 1 tt (genotypic 1 : 2 : 1).
2. If T is fully dominant the dominant phenotype occurs in 3 out of 4 cases (TT, Tt, Tt).
3. Recessive phenotype in 1 of 4 (tt). Phenotypic ratio is therefore 3 : 1.
_Source: Maharashtra Balbharati Std XII Biology, Ch 3 "Inheritance and Variation" §3.3_
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