Principles of Biology homework 4 March 2011, Winslow

Name:

This homework is due on Tuesday, 22 March 2011.

1. (10 points) Consider the genes for seed color and shape in the garden pea investigated by Mendel. Yellow (G) is dominant to green (g), and round (W) is dominant to wrinkled (w). If you were to cross an individual of genotype GgWw with an individual of genotype ggww, what genotypes and phenotypes would be expected in the offspring? Use a Punnett square to calculate expected genotypic and phenotypic ratios for the offspring. How might these ratios be different if the two genes were linked; i.e., close together on the same chromosome?

2. (10 points) Red-green color blindness in humans is a recessive X-linked trait. If a woman with red-green color blindness marries a man with normal vision, what phenotypes would you expect in the offspring? Consider both sex and color blindness as aspects of phenotype. Use a Punnett square to calculate genotypic and phenotypic ratios.

3. (10 points) Examine the pedigree chart below. The dark-filled symbols indicate the presence of a genetic disorder. Do you think the disorder is autosomal, X-linked, or Y-linked? Do you think the disorder is likely to be dominant or recessive?