Biology Hour____ Name___________________________________
Dr. Wexler
Drosophila Mystery Cross
3/30/09

What was done:

You and your partner prepared two vials of fly medium. The purpose of the study is to determine the F1 phenotype and genotype ratios the result when red-eyed and white-eyed fruit flies are crossed. Red eye color is dominant and white eye color is recessive.

For the first cross, virgin white-eyed females (WEF) and red-eyed males (REM) were mated.

For the second cross, pure-breeding virgin red-eyed females (REF) and white-eyed males (WEM) were mated.

The problem:

The instructor labeled the mating vials “Vial 1” and “Vial 2” but neglected to record which cross was performed in which vial.

Your first task:

Determine which parent flies were combined in each of the two vials by analyzing the phenotypes of
their offspring (F1 generation).

Create a results table in the space below in which you record both the eye color and gender of each fly.

Be neat! Record your results on a separate sheet of paper before constructing your table here.

Results:

Your second task:
Look at your data for the two crosses. You should see several patterns. Can you figure out what those patterns are? Don't say no! Say yes and write your answers below:

1. What two patterns do you see for the first cross: WEF x REM?

A. Pattern 1

B. Pattern 2

1. What two patterns do you see for the second cross: REF x WEM?

A. Pattern 1

B. Pattern 2

Your third task:
1. What did you expect to see for a cross between a homozygous dominant (red-eyed) fly and a homozygous recessive (white-eyed) fly? Draw a Punnett square to illustrate your reasoning.

2. One of your crosses should be as expected, but the other should not be as expected.

A. Which cross was as expected?

B. Which cross was not as expected?

3. Propose a genetic explanation for that difference.

Your final task: Mystery solved!

Based on the analysis of your results, which vial contained which cross?

A. Vial 1

B. Vial 2