genetics (dihybrid cross and probabilities )/Genetics Spring 2017, Section 202-3
Problem Set 2 Due: Monday 1/30/17 Please show your work to get full credit.
1. 1. In cats, curled ears (Cu) result from an allele that is dominant over an allele for normal ears (cu). Black color results from an independently assorting allele
(G) that is dominant over an allele for gray (g). A gray cat homozygous for curled ears is mated with a homozygous black cat with normal ears. All the F1 cats are
black and have curled ears. a. If two of the F1 cats mate, what phenotypes and proportions are expected in the F2? Please use Punnett Square to show your work. b. An
F1 cat mates with a stray cat that is gray and possesses normal ears. What phenotypes and proportions of progeny are expected from this cross? Please use branch
diagram to show your work.
2. In cucumbers, dull fruit (D) is dominant over glossy fruit (d), orange fruit (R) is dominant over cream fruit (r), and bitter cotyledons (B) are dominant over
nonbitter cotyledons (b). The three characters are encoded by genes located on different pairs of chromosomes. A plant homozygous for dull, orange fruit and bitter
cotyledons is crossed with a plant that has glossy, cream fruit and nonbitter cotyledons. The F1 are intercrossed to produce the F2. What percentage of the F2
offspring will have the following phenotype? a. Dull, orange fruit and bitter cotyledon b. Dull, cream fruit and nonbitter cotyledon c. Glossy, cream fruit and
nonbitter cotyledon d. Glossy, orange fruit and bitter cotyledon
3. Do book problem 38 (page 73).
4. In sesame, the one-pod condition (P) is dominant to the three-pod condition (p), and normal leaf (L) is dominant over wrinkled leaf (l). The two characters are
inherited independently. A cross between two members of the F1 generation produces the following progeny: 318 one-pod normal, 185 one-pod wrinkled, 323 three-pod
normal and 184 three-pod wrinkled. Determine, using chi-square analysis whether the data fits the typical 9:3:3:1 ratio. Show your work.
5. In a family of seven children, what is the probability of obtaining the following numbers of boys and girls? a. Six girls and one boy b. Four boys and three girls
c. Four girls and three boys
