Experiment 1: Punnett Square Crosses:-

General Questions:
1. In a species of mice, brown fur color is dominant to white fur color. When a brown mouse is crossed with a white mouse all of their offspring have brown fur. Why did none of the offspring have white fur?

2. Can a person's genotype always be determined by their phenotype? Why or why not?

3. Set up and complete Punnett squares for each of the following crosses: (remember Y = yellow, and y = blue)
A. Y Y and Y y
B. YY and yy

4. What are the resulting phenotypes of all the offspring of these two Punnett squares?

5. Are there any blue offspring? Why or why not?

6. Set up and complete a Punnett square for a cross of two of the F1 from Step 1B above.

7. What are the genotypes of the F2 generation in this Punnett square?

8. What are the phenotypes of the F2 generation in this Punnett square?

9. Identify the four possible gametes produced by the following individuals:
A. YYSs: ______ ______ ______ ______
B. YySs: ______ ______ ______ ______
C. Create a Punnett square using these gametes as P:
D. Determine the genotypic ratio of the F1 generation:
E. Determine the phenotypic ratio of the F1 generation:

Questions for Part 2: Monohybrid Cross:
1. How much genotypic variation do you find in the randomly picked parents of your crosses?

2. How much genotypic variation is there in the offspring?

3. How much phenotypic variation is there in the offspring?

4. Is the ratio of observed phenotypes the same as the ratio of predicted phenotypes? Why or why not?

5. Pool all of the offspring from your five replicates. How much phenotypic variation do you find?

6. What is the difference between genes and alleles?

7. Organisms heterozygous for a recessive trait are often called carriers of that trait. What does that mean?

8. In peas, green pods (G) are dominant over yellow pods.
A. If a homozygous dominant plant is crossed with a homozygous recessive plant, what will be the phenotype of the F1 generation?

B. If two plants from the F1 generation are crossed, what will the phenotypes of their offspring be?

Questions for Part 3: Dihybrid Cross:
1. How similar are the observed phenotypes in each replicate?

2. How similar are they if you pool your data from each of the five replicates?

3. Is it closer or further from your prediction?

4. Did the results from the monohybrid or dihybrid cross most closely match your predicted ratio of phenotypes?

5. Based on these results, what would you expect for a cross involving 5, 10, or 20 independently sorted genes?

6. In cats, short hair (S) is dominant over long hair (s) and white coat (W) is dominant over non-white coat (w). Show a cross between an all-white cat with long hair and a non-white, short-haired cat. Both cats are homozygous for all traits.

A. What would be the expected phenotypic ratio of the F1 offspring?
B. What would be the expected phenotypic ratio of the F2 offspring?