Need help assigning genotypes to Drosophila

Question

The white eye mutation studied by Thomas Hunt Morgan is X-linked and recessive to wild-type red eyes. When true-breeding white-eyed males carrying the white mutation were crossed with true-breeding purple-eyed females, all the F1 progeny had wild-type (red) eyes. When the F1 progeny were intercrossed, the F2 progeny emerged in the following ratio:

3/8 wild-type females

1/4 white-eyed males

3/16 wild-type males

1/8 purple-eyed females

1/16 purple-eyed males

Match the correct genotype with each individual listed below:

___ 1. P Generation Male

___ 2. P Generation Female

___ 3. F1 Generation Male

___ 4. F1 Generation Female

___ 5. F2 Generation Purple-eyed Female

___ 6. F2 Generation White-eyed Male

___ 7. F2 Generation Wild-type Male

___ 8. F2 Generation Purple-eyed Male

___ 9. F2 Generation Wild-type Female

a. none of the above

b. w+_; p+_

c. w+/w+; p/p

d. w/Y; p+/p+

e. w+/_; p/p

f. w+/Y; p+/p

g. w+/w; p+/p

h. w/Y; _ _

i. w+/Y; p/p

j. w+/Y; p+/_

Answer 1

This seems like a homework problem so I will not give you the full answer but I will give you some background information that should help you solve it.

This is a bit of a complicated genetics problem featuring both sex linkage and a dihybrid cross. You need to keep in mind when answering that you have 2 different genes here. One for wild type/white eyes (and white eyes lack pigment). The other gene is for the proper red pigment of wild type eyes. The dominant is normal pigment or red eyes and the recessive is purple eyes. White eyes would not be affected by the second gene because of its lack of pigment. Therefore, the male white eyed parent must be carrying the dominant version of the gene in order for red eyes to occur in any generation of the progeny since purple eyes are recessive.