Question

Let Y = yellow and y = green, and R = round and r = wrinkled. You cross YYRR peas with yyrr peas. All of the F1 individuals are yellow and round with a genotype of YyRr. You then perform an F2 cross and get the expected 9:3:3:1 phenotypic ratio. What proportion of the F2 plants are expected to be heterozygous for both traits?

Answer 1

Answer:

1/4

Explanation:

Given that the F2 cross produces offspring according to the expected 9:3:3:1 ratio.

YyRr X YyRr:

Let us break the dihybrid cross into individual monohybrid crosses.

Yy X Yy :

    Y     y

Y  YY  Yy

y   Yy   yy

2/4 or 1/2 of the offspring are heterozygous for the trait.

Similarly, in Rr X Rr cross, 1/2 of the offspring are heterozygous for the trait.

Together, 1/2 * 1/2 = 1/4 of F2 plants are expected to be heterozygous for both traits.