Question

You perform a test cross of the dihybrid AaBb and score the phenotypes of 1000 progeny. Assuming independent assortment, how many of the progeny do you expect to display the dominant phenotype for both the A and B genes?

- 750
- 100
- 250
- 500
- 200

Answer 1

250.

Step-by-step explanation:

A test cross would cross the genotype AaBb with homozygous recessive genotype aabb. The cross between AaBB x aabb would produce progeny in 1:1:1:1 ratio. So, the proportion of the progeny expressing both dominant traits (AaBb) is 1/4.

Therefore, out of the total 1000 offspring, 1/4 x 1000= 250 would express the dominant phenotype for both A and B genes.