2021 · Q14
In pea, a pure tall plant (TT) is crossed with a short plant (tt). What will be the ratio of pure tall plants to short plants in the F generation? 2
General KnowledgeBiology
- A1 : 1
- B1 : 3
- C3 : 1
- D2 : 1
Explanation
The cross TT x tt produces an F1 generation that is entirely heterozygous tall (Tt), since tallness is dominant. Selfing the F1 (Tt x Tt) gives the genotypic ratio 1 TT : 2 Tt : 1 tt. 'Pure tall' means the homozygous dominant genotype TT, which forms 1 part, while short plants are tt, also 1 part - so the ratio of pure tall plants to short plants is 1:1. The familiar 3:1 figure is the phenotypic ratio of all tall plants (TT + Tt) to short plants and is not what this question asks.