Question

1. You are tracking two genes in drosophila (body color and eye color). To determine whether the traits are on the same chromosome you set-up the following cross: Orange body & Red eyes (w+/w;b+/b) x White body & Brown eyes (w/w;b/b) Predict the phenotype ratios of the offspring if the genes are on two different chromosomes (include the phenotypes). Show how you determined this.

Answer 1

Answer:

Phenotypic ratio:

In this cross among 16 offsprings,

4 offspring phenotypically produced (w+wb+b) Orange body & Red eyes

4 offspring phenotypically produced (w+wbb) Orange body & Brown eyes

4 offspring phenotypically produced (wwb+b) White body & Red eyes

4 offspring phenotypically produced (wwbb) White body & Brown eyes

Proportion is:   4  :  4 : 4 : 4

Explanation:

Orange body & Red eyes (w+/w;b+/b) x White body & Brown eyes (w/w;b/b)

                                               w+wb+b × wwbb-----------(1)

Chromosomes become half and alleles become separated. Gametes produced from each organism due to meiosis are shown below.

                    w+b+,  w+b,  wb+ and wb × wb,  wb,  wb and wb--------------(2)

Mating of these alleles are represented below in the form of checkerboard.

                 w+b+            w+b             wb+          wb

wb           w+wb+b      w+wbb        wwb+b       wwbb

wb           w+wb+b      w+wbb        wwb+b       wwbb

wb          w+wb+b      w+wbb        wwb+b       wwbb

wb           w+wb+b      w+wbb        wwb+b       wwbb

Answer

Phenotypic ratio

In this cross among 16 offsprings,

4 offspring phenotypically produced (w+wb+b) Orange body & Red eyes

4 offspring phenotypically produced (w+wbb) Orange body & Brown eyes

4 offspring phenotypically produced (wwb+b) White body & Red eyes

4 offspring phenotypically produced (wwbb) White body & Brown eyes

Proportion is:   4  :  4 : 4 : 4