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

Answer:

rosy-eye (recessive) = r ; Wild-eye (dominant)= R

Fork-bristled (recessive)= f; wild-bristles (dominant)= F

(rosy-eyed, wild-type bristles) X (fork-bristles, wild-type eyes) ---Partents

rrFF X RRff

rF           Rf --------------gametes

   RrFf (wild type for both traits)---F1

F1 X F1

RrFf x RrFf

RF

Rf

rF

rf

RF

RRFF(wild type for both traits)

RRFf (wild type for both traits)

RrFF (wild type for both traits)

RrFf (wild type for both traits)

Rf

RRFf (wild type for both traits)

RRff (fork-bristles)

RrFf (wild type for both traits)

Rrff (fork-bristles)

rF

RrFF (wild type for both traits)

RrFf (wild type for both traits)

rrFF (ros-eye)

rrFf (ros-eye)

rf

RrFf (wild type for both traits)

Rrff (fork-bristles)

rrFf (ros-eye)

rrff (ros-eye, fork-bristles)

306 wild-type, 94 rosy-eyed, 102 fork-bristled, and 33 forked-bristled and rosy-eyed flies = 9:3:3:1

As the F2 ratio indicates Dihybrid phenotypic ratio (9:3:3:1), so the genotypes may be indicated as dihybrid cross.