Question: 145. Genes R and Y follow independent assortment. If RRYY produce round yellow seeds and rryy produce wrinkled green seeds, what will be the phenotypic ratio of the F2 generation?
(1) Phenotypic ratio-1:2:1
(2) Phenotypic ratio- 3: 1
(3) Phenotypic ratio- 9: 3: 3: 1
(4) Phenotypic ratio-9:7
Answer: Option (3)
Explanation:
The cross is between RRYY (round yellow) and rryy (wrinkled green).
The F₁ generation will all be RrYy and will show round yellow seeds because both round (R) and yellow (Y) are dominant traits.
When F₁ individuals RrYy are self-crossed:
– Each gene pair (R/r and Y/y) assort independently as per Mendel’s law.
– The dihybrid cross RrYy \times RrYy produces four phenotypes in the classic ratio:
9 Round Yellow : 3 Round Green : 3 Wrinkled Yellow : 1 Wrinkled Green
Thus, the phenotypic ratio in the F₂ generation is 9:3:3:1.