Figure 1.

(A) Using the yellow⁺ minichromosome Dp(1;f)8-23 to rescue yellow mutants. This minichromosome was created by a duplication of part of the tip of the X chromosome where the y locus resides. Minichromosome 8-23 and related minichromosomes are the smallest chromosomes known to be transmitted in eukaryotes. 8-23 carries the entire endogenous y locus with all of its normal flanking DNA, which includes previously characterized regulatory regions that act as enhancers. Approximately 12 wild-type genes are carried on the minichromosome, as well as two rosy⁺ P-element insertions. The P elements and the yellow and achaete loci are shown. The striped rectangle is ∼1000 kb of centromeric heterochromatin. (B) The crossing scheme used to generate experimental and control males. This one-generation crossing scheme takes advantage of the y⁺ locus located in minichromosome 8-23, and it was used for all of the experiments reported in this article. To generate completely outbred and isogenomic males, we crossed females (with one genetic background, in pink) with the y mutant allele of interest (y⁻) to males (with another genetic background, in blue) that were y¹; ry⁵⁰⁶; 8-23, ry⁺ y⁺. (The y⁺ minichromosome is shown by a black/yellow striped line.). All sons receive the same X chromosome carrying a y mutant from their mother, and ∼75% of the males receive the y⁺ minichromosome from their father (see materials and methods). In this manner, y⁻ (“experimental”) and y⁻ ; y⁺ (“control”) males are generated for analysis. Experimental and control males have the same set of parents and develop in the same set of bottles, and the behavior of both groups is measured simultaneously in the Copulatron.