We will be using the Virtual Fly Lab, which will allow us to spend less time collecting data and more time analyzing it. Unfortunately, the software has been updated since the lab manual was written, so corrected instructions are included in the back of this packet. Follow the instructions for mating flies with one or two mutant traits. Try recording results in your electronic notebook and crossing the F₁ flies. You should be comfortable with the software before proceeding with the assignment. The program counts the flies and tabulates the data. Now that you have mastered the ² analysis, the program quickly does it for you! You are left with designing the crosses, selecting the ratios and identifying and mapping linked genes.

1. Determine the mode of inheritance of the following traits. Keep accurate records of your crosses on the data sheets provided! List the cross(es) you have done to determine the mode of inheritance, as well as the approximate ratios of offspring (1:2:1 as opposed to 1.06:2.07:0.94).

bar eyes
eyeless
sepia eyes
black body
miniature wings
vestigial wings
shaven bristles
spineless bristles

You may wish to check your answers before proceeding to make sure you are on the right track!

2. Drosophila melanogaster has four chromosome pairs; one of the chromosomes is very tiny, so few genes are located on it, and they are all closely linked. The eight traits listed above have been carefully chosen because they are located on each of the chromosomes (two per chromosome). Your goal is to determine which pairs are linked, and the map distances between them.

A. Before proceeding, detail the strategy you plan to use to test for linkage. (Note: there is a real key about which of these genes should be tested in the Virtual Fly program - it is a limitation of the program that should save a number of steps in the process.)

B. Include the data from the crosses that show linkage, then calculate linkage distances. You should have four pairs of linked genes.

3. Next, you should map the following genes by following the steps below:

A. Determine mode of inheritance as in #1 above.
B. Identify which linkage group the gene is in. (Include data of cross.)
C. Conduct a three factor cross with the pairs of linked genes from #2.
D. Identify the order of the genes, as well as m.u. between each of the pairs.

Genes to map:

dichaete wings
forked bristles
sable body
tan body
yellow body
lobe eyes
purple eyes
star eyes
white eyes
dumpy wings

4. Analysis: Are the alleles for body color or eye color at the same gene locus? How do you know?

5. Which chromosome is the longest? Shortest? How do you know?