Chapter 5, Problem 6P

In Drosophila, the map positions of genes are given in mapunits numbering from one end of a chromosome to theother. The $\text{X}$ chromosome of Drosophila is $\text{66 m}\text{.u}\text{.}$ long.The $\text{X-linked}$ gene for body color $\text{—}$ with two alleles, $\text{y+}$ forgray body and y for yellow body $\text{—}$ resides at one end ofthe chromosome at map position $\text{0}\text{.0}$. A nearby locus foreye color, with alleles $\text{w+}$ for red eye and w for white eye, is located at map position $\text{1}\text{.5}$. A third X-linked gene, controlling bristle form, with $\text{f+}$ for normal bristles and f forforked bristles, is located at map position $\text{56}\text{.7}$. Each generesides on the X chromosome, and at each locus the wildtype allele is dominant over the mutant allele.

a. In a cross involving these three $\text{X-linked}$ genes, do youexpect any gene pair(s) to show genetic linkage? Explainyour reasoning.

b. Do you expect any of these gene pair(s) to assort independently? Explain your reasoning.

c. A wild $\text{-}$ type female fruit fly with the genotype $\text{y+w+f/ ywf+}$ is crossed to a male fruit fly that has yellow body, white eye, and forked bristles. Predict the frequency of each progeny phenotype class produced by this mating

d. Explain how each of the predicted progeny classes isproduced.