White (w) & Yellow (y) are both on the X chromosome and only 1.5 M.U. apart. Let us see if the data obtained fits with a sex-linked, linked gene (at 1.5 M.U.), recessive inheritance model.

1.      Determine expected frequencies of each individual progeny possibility based on the 1.5 M.U. distance. Do this by showing a punnet square for frequencies. This one is challenging since it involves two genes both on the X chromosome and we are going to assume that crossing over does not happen in males. However, we are still going to ignore the effects of multiple crossover events.

a.       (1.5 points) First, determine what gametes each adult of the F1 can produce (don't calculate probabilities yet). You may need to consider sex, linkage, and lack of male crossing over to determine this. Remember this is class data so the P generation was affected males crossed to homozygous wild type females.

b.      (1 point) Which gametes represent the "parental" type? Which are "non-parental," and so therefore are a result of crossing over?

c.       (1.5 point) Construct the punnet square showing the genotype outcomes of this F1 sibling cross (don't calculate probabilities yet).

d.      (1.5 points) Construct a punnet square showing the expected genotype probabilities/frequencies (based on 1.5 M.U.) and then calculate and show the phenotype frequencies. Remember how recombination frequency relates to the frequency of parental and non-parental gametes.

2.      (1 point) Determine the expected number of flies of each category.