Genetics problem sets:

Homework set 1, Due week of September 12

To do on your own: Chapter 2 (part 1): 3, 4, 5, 8, 11, 15

To hand in (9/12/05):
Show all of your work, to get partial credit.

  1. Mendel crossed pure breeding round-seeded, purple-flowered peas with a pure breeding wriinkled white pea to produce an F1. The round allele (R) is dominant to wrinkled (r) and the Purple allele (P) is dominant to white (p). Those two genes are on separate chromosomes. Diagram those chromosomes:
    1. at metaphase 1 of meiosis in the heterozygous F1 plant
    2. at metaphase of mitosis in the F1 plants
    3. Diagram all possible gametes produced by those F1 peas.
  2. In the cross Aa Bb Cc x Aa Bb Cc, in which all three genes show independent assortment,
    1. what proportion of offspring are expected to be heterozygous for all three genes?
    2. How does it change if the cross is Aa Bb Cc x Aa bb cc?
    3. Assuming that alleles with capital letters are dominant, what proportion of the offspring in the first cross will have the phenotype A- B- cc?
  3. Absence of the enzyme alpha-1-antitrypsin is associated with a high risk of developing emphysema. The deficiency is usually caused by having two copies of the recessive allele PI-Z. A phenotypically normal man whose father died of emphysema associated with PI-Z marries a normal woman with no family history of the disease. They consider having a child.
    1. Draw the pedigree specified by this scenario.
    2. A small proportion of the general population are carriers for the allele, even though they have no obvious family history. If the couple's first child is homozygous for PI-Z, what is the probability that their second child will have the disease?

Sept. 6

To do on your own: Chapter 2 (part 2): 24, 29, 32, 33, 39, 41

To hand in (9/12/05)

  1. Vermilion eyes is an X-linked trait in the fruit fly Drosophila melanogaster. X+ chromosomes carry the allele for normal (brick-red) eye color and Xv chromosomes carry the allele for vermilion eyes.
    Identify the genotype of each of the individuals in the following pedigree. Shaded symbols mean that the fly has vermilion eyes, open symbols are for flies with normal eyes. If more than one genotype is possible, give the probability of each.
  2. How would you set up crosses to determine if a trait was X-linked vs Y-linked? (You can make up an imaginary disease if you want, or you could use a trait like eye color). Show
    1. the genotypes of the parents that you would choose
    2. the predicted offspring genotypes and phenotypes if the gene was X-linked
    3. the predicted offspring genotypes and phenotypes if the trait was Y-linked.