Segregation of different traits

Assignment 1: 
Segregation and Chi-Squared

Part A: Segregation of different traits

Cross a female with one mutation to a male with a different mutation. You can pick anything you want except Curly or Dichaete wings, we will use them later. Also remember not to pick two mutations that affect the same structure like two eye color mutations. ONLY ONE MUTATION WITH A WILD TYPE

1. In the F1, are either of the mutations you selected dominant? Why?
2. Does the mutation appear to be sex linked? Why?

Cross two of the F1 progeny and observed the ratios of the resulting progeny.

3. Does the ratio observed agree with two independently assorting genes? Why? Use a chi-squared test to support your conclusions and suggest an alternative explanation if your data do not fit independent assortment.

Part B: Test your conclusions with another experiment

For each mutant you selected above, we will identify its chromosome by crossing to a tester strain with known, dominant markers for Chromosomes 2 and 3. The segregation pattern will help you determine the chromosome on which your mutation resides. Chromosome 1 is the X chromosome, which would show sex linkage, so this cross will let you identify mutations on the three largest chromosomes covering most genes.

Step 1. Construct tester strain female. Select Curly wings (Cy) from Wing Shape and Dichaete (D) from Wing Angle. These are dominant mutations: Cy is on Chromosome 2, D is on Chromosome 3.

Step 2. Construct unknown mutant male.

Pick one of the mutations you used in Part A, but only one and stick with it in later crosses.

Step 3. Cross the P1 flies you just constructed. If you do not see your mutant phenotype in the F1, it is recessive.

Step 4. Perform a testcross to find your mutant. Pick one of the Cy;D males from the F1 for mating. It is carrying the dominant chromosome markers, but also is heterozygous for your recessive mutation. Construct a female who has the mutation you originally picked for the P1, but is wildtype for everything else. Mate the flies and look at the progeny.

You should find that your mutation reappeared. The male from step 4 carried the mutation as a heterozygote. If the mutation is on Chromosome 2, then he would pass on either the Cy chromosome or the recessive mutant chromosome, but you would not find progeny that were both Cy and mutant. Similar logic applies to Chromosome 3 and the D mutation. If there is a difference between the appearance of your mutation depending upon the sex, then the mutation may reside on the X chromosome.

Try to use Punnett squares to diagram the crosses you performed based on where you think your mutation is located. You can use the Analyze tab to perform a chi-squared test. Make sure the ratios you choose for you hypothesis fit the predictions from your Punnett squares.