Assignment 2: Sex Linkage
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.
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?
Now perform a reciprocal cross by crossing a tan male to a wildtype female. Do you see the same results in the F1 and F2 as before? Try diagramming your F2 results for both crosses. Use the Prediction chi-squared tool to test your hypothesis.
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