Intro to Molecular, Cellular and Developmental Biology: Spring 2010

You cross wild, gray-colored mice with white (albino) mice. In the first generation, all are gray. From many litters, you obtain in the F₂ 198 gray and 72 white mice.

1. Propose a model to explain these results.
2. On the basis of this model, diagram the cross and compare the observed results with those expected (e.g., use a Chi-square test).

A woman has a rare abnormality of the eyelids called ptosis, which makes it impossible for her to open her eyes completely. The condition has been found to depend on a single dominant allele (P). The young woman's father had ptosis, but her mother had normal eyelids. Her father's mother had normal eyelids. (a) What are the probable genotypes of the woman, her father, and her mother? (b) What proportion of her children will be expected to have ptosis if she marries a man with normal eyelids?

Short hair in rabbits (S) is dominant over long hair (s). The following crosses are carried out, producing the progeny shown. Give all possible genotypes of the parents of each cross.

In cucumbers, orange fruit color (R) is dominant over cream fruit color (r). A cucumber plant homozygous for orange fruits is crossed with a plant homozygous for cream fruits. The F₁ are intercrossed to produce the F₂.

1. Give the genotypes and phenotypes of the parents, the F₁, and the F₂.
2. Give the genotypes and phenotypes of the offspring of a backcross between the F₁ and the orange parent.
3. Give the genotypes and phenotypes of the offspring of a backcross between the F₁ and the cream parent.