Question

With independent assortment, the ratio of phenotypes in the F2 generation of a cross between true-breeding strains (AA bb x aa BB) can be described as 9:3:3:1 when A and B are dominant over a and b. To what phenotype does the "9" in the ratio refer?

a. recessive for both traits
b. dominant for one trait and recessive for the other
c.dominant for the A trait and recessive for the B trait
d. dominant for both traits

Answer 1

The "9" in the 9:3:3:1 ratio refers to offspring that are dominant for both traits, which occurs with a probability of 9/16 when considering two traits with independent assortment.

Step-by-step explanation:

The "9" in the 9:3:3:1 phenotypic ratio refers to the phenotype that is dominant for both traits. This ratio emerges from the cross between true-breeding strains (AA bb x aa BB) when A and B are dominant alleles over a and b. Independent assortment ensures that alleles for different traits are transmitted to offspring independently of each other. Combining the probabilities for the dominant phenotypes of each trait, both texture and color in this context, we apply the product rule. Since each trait has a 3:1 dominant to recessive ratio, the probability of an offspring being dominant for both traits is (3/4) × (3/4) = 9/16.

Answer 2

B. Dominant for one trait and recessive for the other

Step-by-step explanation:

using the Punnetts square for the question above, the 9 in the ration refers to a dominant for both traits such as AABB, AaBb.

while the 3: 3 refers to a dominant for a single trait and recessive for one such as AAbb, Aabb, aaBB, aaBb

and the 1 refers to recessive for both traits such as aabb.