Principles Of Mendelian Inheritance

In a dihybrid cross between true-breeding round yellow (RRYY) and wrinkled green (rryy) pea plants, the F₂ ratio for round:wrinkled seeds is 3:1.

(A) 9:1 - Incorrect: This doesn't represent any standard Mendelian ratio.

(B) 3:1 - Correct: When considering only seed shape (ignoring color), the monohybrid ratio reasserts itself (3 round : 1 wrinkled).

(C) 9:3 - Incorrect: This represents partial phenotypic ratio (round yellow + round green).

(D) 3:3 - Incorrect: This would suggest equal proportions, which isn't observed.

The correct answer is (B) 3:1, demonstrating Mendel's Law of Segregation for a single trait (round vs wrinkled) within a dihybrid cross.