Answer:
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.