Chapter 19, Problem 15P

To determine the focus of action of boss⁺, researchers performed a mosaic experiment like the one shown in Fig. 19.11: Ommatida mosaic for w⁺boss⁺ and w^- boss^- photoreceptors were generated by mitotic recombination using FLP/FRT.

a.

Describe the appearance of the mosaic ommatidia (which cells are w+ and which are w-) that have a wild-type phenotype (R7 present) and that have a boss- mutant phenotype (R7 absent). What is the focus of action of the boss+ gene?

b.

Although the boss gene is located on chromosome 3, it was still possible to use the w+ gene as a marker for boss+ cells. This was achieved by using flies in which the endogenous white gene on the X chromosome was mutant and that carried a P[w+] transgene on chromosome 3. Diagram the chromosomes used, including in your diagram the positions of the FRTs, the P[w+], boss- and boss+ alleles, and the mitotic crossover. Show also how the chromosomes segregate into daughter cells to generate the mosaics.