Assignment 5

For many of the mutations that can be studied using FlyLab, it does not matter which parent carries a mutated allele because these mutations are located on autosomes. Reciprocal crosses produce identical results. When alleles are located on sex chromosomes, however, differences in the sex of the fly carrying a particular allele produce very different results in the phenotypic ratios of the offspring. Sex determination in Drosophila follows an X-Y chromosomal system that is similar to sex determination in humans. Female flies are XX and males are XY. Design and perform the following crosses to examine the inheritance of sex linked alleles in Drosophila.


1 .		Cross a female fly with a tan body with a wild-type male. What phenotypes and ratios did you observe in the F₁ generation? Mate two F₁ flies and observe the results of the F₂ generation. Based on what you know about Mendelian genetics, did the F₂ generation demonstrate the phenotypic ratio that you expected? If not, what phenotypic ratio was obtained with this cross?

2 .		Perform a second experiment by crossing a female fly with the vestigial wing size mutation and a white-eyed male. Describe the phenotypes obtained in the F₂ generation. Examine the phenotypes and sexes of each fly. Is there a sex and phenotype combination that is absent or underrepresented? If so, which one? What does this result tell you about the sex chromosome location of the white eye allele?