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?

4

Explanation:

The number of progeny expected to display the dominant phenotype for both the A and B genes should be  4.

A test cross usually involves crossing an individual whose zygosity is in doubt with an individual that is recessive for both alleles so as to ascertain the zygosity of the former. Hence, for a test cross involving AaBb:

             AaBb     x     aabb

Progeny:

4 AaBb

4 Aabb

4 aaBb

4 aabb

Therefore, the number of progeny expected to display the dominant phenotype for both the A and B genes is 4.