Principle of Inheritance and VariationMediumBloom L3
Question
The ratio of phenotypes in F2 of a monohybrid cross is
Options
A.3 : 1
B.1 : 2 : 1
C.9 : 3 : 3 : 1
D.2 : 1
Solution
Sol.(a) [Key Concept: Monohybrid Cross — F2 Phenotypic Ratio] The phenotypic ratio in F2 of a monohybrid cross (with complete dominance) is 3:1 (three dominant phenotype : one recessive phenotype). Cross: Aa × Aa → 1/4 AA : 2/4 Aa : 1/4 aa. Phenotypically: AA and Aa both show dominant phenotype = 3/4 dominant; aa = 1/4 recessive = 3:1. The 1:2:1 ratio is the GENOTYPIC ratio (or phenotypic ratio with incomplete dominance); 9:3:3:1 is F2 dihybrid ratio; 2:1 is lethal gene ratio.
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