Question

In a dihybrid cross between a true breeding round yellow seeded and true breeding wrinkled green seeded pea plant, the ratio of segregation of round and wrinkled seed traits in F2 is:

• A. 9:1
• B. 3:1
• C. 9:3
• D. 3:3

Hint:

Mendelian principles explain predictable inheritance patterns in dihybrid crosses.

Answer 1

The Correct Option is B

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.

Answer 2

In a dihybrid cross, two traits are considered. For pea plants, the round (R) and wrinkled (r) seed shape and yellow (Y) and green (y) seed color are studied. A cross between round yellow-seeded (RRYY) and wrinkled green-seeded (rryy) plants produces F1 hybrids (RrYy), all with round yellow seeds. In the F2 generation, the segregation of the seed shape traits (round and wrinkled) follows a 3:1 ratio (dominant to recessive) because of Mendelian inheritance.

Option (B) is correct because the ratio of round to wrinkled seeds in F2 generation is 3:1.