A rosyeyed Drosophila with wildtype bristles was crossed wit

A rosy-eyed Drosophila with wild-type bristles was crossed with a forked Drosophila with wild-type eyes. The F1 were wild type for both traits, whereas the F2 consisted of 306 wild-type, 94 rosy-eyed, 102 fork-bristled, and 33 forked-bristled and rosy-eyed flies. What are the genotypes of the parents and how do you know?

Solution

Assume that the gene coding for wild-type eyes is, A and the gene coding for rosy-eyes is, a; A is dominant over a. Similarly, the gene coding for wild type bristles is, B and the gene coding for forked bristles is b; B is dominant over b.

Given that, cross between a rosy-eyed Drosophila with wild-type bristles (aa BB) and forked Drosophila with wild-type eyes (AA bb) had all wild type progeny.

Parental genotypes:

aa BB* AA bb --à Aa Bb (100% wild type) ---à F1

The self-cross of F1 will have the progeny with the following genotypes:

Aa Bb* Aa Bb --à A_ B_ (9/16, wild type), A_ bb (3/16, wild type eyes, forked bristles), aa B_ (3/16, rosy eyes, wild type bristles), aa bb (1/16, rosy eyes, forked bristles)

Thus, the parents are true breeders, their genotypes are, aa BB and AA bb