Chapter 5, Problem 24P

The boss in your laboratory has just heard of a proposal by another laboratory that genes for eye color and the length of body bristles may be linked in Drosophila. Your lab has numerous pure-breeding stocks of Drosophila that could be used to verify of refute genetic linkage. In Drosophila, red eyes $\left({\text{c}}^{\text{+}}\right)$ are dominant to brown eyes $\left(\text{c}\right)$, and long bristles $\left({\text{d}}^{\text{+}}\right)$ are dominant to short bristles $\left(\text{d}\right)$. Your lab boss asks you to design an experiment to test the genetic linkage of eye color and bristle-length genes, and to begin by crossing a pure-breeding line homozygous for red eyes and short bristles to a pure-breeding line that has brown eyes and long bristles.

a. Give the genotypes of the pure-breeding parental-files, and the genotype $\left(\text{s}\right)$ and phenotype(s) of the ${\text{F}}_{\text{1}}$ progeny they produce.

b. In your experimental design, what are the genotype and phenotype of the line you propose to cross to the F₁ to obtain the most useful information about genetic linkage between the eye color and bristle-length genes? Explain why you make this choice.

c. Assume the eye color and bristle-length genes are separated by $\text{28}$ $\text{m}\text{.u}$. What are the approximate frequencies of phenotypes expected from the cross you proposed in part $\left(\text{b}\right)$?

d. How would the results of the cross differ if the genes are not linked?