Question

If AABB is crossed to aabb and the F1 is testcrossed, what percent of the testcross progeny will be aabb if the two genes are

A) unlinked
B) completely linked
C) 10 map units apart
D) 24 m.u. apart

Answer 1

The percentage of testcross progeny that will be aabb in a dihybrid cross between AABB and aabb flies depends on the linkage between the two genes.

Step-by-step explanation:

In a testcross between the F₁ generation of a cross between AABB and aabb flies, the percentage of progeny that will be aabb depends on the linkage between the two genes.

A) If the genes are unlinked, the F₂ generation will have a 1:1:1:1 ratio of genotypes, so 25% of the testcross progeny will be aabb.

B) If the genes are completely linked, meaning they are located very close together on the same chromosome, there will be no recombination between them and all F₂ progeny will have the same genotype as the parent (AABB).

C) If the genes are 10 map units apart, there will be a 10% recombination frequency between them, so 10% of the testcross progeny will be aabb.

D) If the genes are 24 map units apart, there will be a 24% recombination frequency between them, so 24% of the testcross progeny will be aabb.