Honor System


Course Topics


Homework Assignment - Mendelian Genetics

100 total points

Use complete sentences in all of your answers where appropriate. If you are stumped by a problem, explain as much as you can to get partial credit.

1. Fat color is determined by a single gene in sheep, and white fat is dominant to yellow fat. At a second gene, normal ears are incompletely dominant to earless, and heterozygotes are short-eared. (10 points total)

a. In some flocks in Scotland, 25% of the lambs have the undesirable yellow fat trait. Can you eliminate the yellow fat trait from these flocks by simply slaughtering all of these animals to prevent them from mating with others in the flock?
b. How would you set up a breeding program to eliminate the yellow fat allele from the flock?
c. This flock is also segregating for all three ear types. How would go about creating a pure-breeding population of normal ear, white fat sheep?

2. The coat of the house mouse can be various colors. Matings were made between black, tan and yellow mice, and the following ratios were observed.

1. Yellow x Tan 1 Yellow : 1 Tan
2. Yellow x Black 1 Yellow : 1 Black
3. Yellow * x Black 1 Yellow : 1 Blackish Tan
4. Yellow** x Tan 1 Yellow : 1 Blackish Tan
5. Yellow* x Yellow** 2 Yellow : 1 Blackish Tan
6. Blackish Tan x Tan 1 Tan : 1 Blackish Tan
7. Blackish Tan x Black 1 Black : 1 Blackish Tan
* The yellow parent was an offspring from cross 1.
** The yellow parent was an offspring from cross 2.

a. Determine the gene action controlling coat color in mice. (20 points)

3. Rats can be either albino or colored, a trait that is controlled by a single gene. Four coat color are possible: gray, yellow, black or cream. For an animal to express one of these colors, they must have a dominant allele at the gene controlling the presence of coat color. Rats recessive at this gene are albino. Four different albino rats were crossed to a pure breeding gray rat. All of the F1 rats from each mating were gray. Then matings of male and female F1 rats within each original cross were made. The F2 data is presented below.

F2 Distribution
Gray Yellow Black Cream Albino
1. 64 0 0 0 22
2. 140 43 45 15 85
3. 92 0 31 0 41
4. 114 39 0 0 49

a. From this data, determine the type of gene action controlling coat color in rat. (10 points)
b. Determine the genotype of each albino line (10 points).

4. A Drosophila geneticist crossed two normal-eyed flies, and all F1 flies had normal eyes. Unexpectedly, a new phenotype, star eye, appeared in the F2 . The geneticist counted the flies, and determined the ratio to be 13 normal eye : 3 star eye. At this point, he realized the type of interaction with which he was dealing. What type of gene action was he observing? (10 points)

5. Go to section 5 of Mendel's original paper, "The First Generation From the Hybrids".

a. In that section, Mendel presents the phenotypic data for the first 10 plants segregating for round and angular (wrinkled) seed (Experiment 1). For each of these 10 plants, statistically test the hypothesis that the data segregates in a 3:1 ratio and state whether the test supports the hypothesis or not. (10 points)
b. Then perform the same test using the data from all 10 plants in your analysis. (5 points)
c. Two other plants segregated 43 round : 2 angular and 14 round : 15 angular. Explain how these results could occur if a single gene is segregating in this population. (5 points)

Use the following link to:

Experiments in Plant Hybridization

to find the necessary data.

6. Aurora and UI 114 are two well established white-flowered cultivars of common bean (Phaseolus vulgaris L.). When these two cultivars are crossed, the F1 offspring have purple flowers. The F2 generation was scored and 221 white-flowered individuals and 259 purple-flowered individuals were observed. Create a hypothesis to explain this observation. Perform a statistical analysis to support the hypothesis you propose. (20 points)