7) Repeat steps 2-6, creating a female cat with a tail, not all white, no white areas, no tabby stripes, and black. Double click the cat face to see the phenotype.

8) Click on once on the male cat icon. It should now be highlighted.

9) Click on the P button at the top of the window. At this point, the cat face icon should be replaced with "Dad"

10 Repeat steps 8 and 9 for the female icon. "Mom" should appear.

Producing offspring.

11) Click the L at the top of the window, and set litter size equal to 5

12) Click the M at the top of the window to carry out the mating. After some meowing, you should see the offspring icons appear in the window. Click OK.

13) The offspring should appear in the window at left, along with their characteristics. As before, you can double click on any cat face icon to see the phenotype.

14) Repeat step 11 until you have 40 offspring.

What proportion of the offspring are black vs. gray?

Can you now determine the genotypes of the parents? If so, explain your reasoning.

If you are still unsure of the parental genotypes, how could you definitively tell? (hint: remember what a test cross is).

If necessary, conduct a test cross to determine parental genotypes. You can eliminate all the unneeded individuals in the window as follows:

15) Click on the individual you wish to save. It should be highlighted.

16) Click on the N in the upper left of the window.

17) Choose selected to retain the highlighted cat(s)

18) Create new cats as necessary for future crosses.

What are the proportions of offspring in your test crosses? What does this tell you about the parental genotypes?

Exercise 2 - Dihybrid crosses

Now that you are familiar with the program, it's now time to try a more complicated cross. This cross will involve a mating between two dihybrid cats. The genes involved are the dense (D) versus dilute (d) gene you just worked with (but this time with orange/cream phenotypes instead of black and gray), and the mackerel (T) versus blotched (t) tabby pattern. These genes are not linked. What does this imply about their location relative to each other?

Mackerel is dominant over blotched, so the genotypes will have the following phenotypes:

TT - Mackerel Tt - Mackerel tt - blotched