First Exam, 1996

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  1. [10 points] Some human populations show a very slight sex bias, with probability 0.53 of a child being a boy and 0.47 of being a girl. Assume these probabilities in your answers for this question.

  2. [5 points] Suppose individuals with genotypes AA and Aa show the "dentist" phenotype, while aa individuals show the "chiropractor" phenotype. When an individual showing the unfortunate "dentist" phenotype is crossed to a "chiropractor" individual, all of their five offspring show the dentist phenotype. What is the probability of this if the "dentist" parent is really Aa?

  3. [5 points] Recall that squirrel monkeys have trichromatic females when both copies of the X chromosome contain different color vision alleles (i.e., heteroyzgous females are trichromatic). Suppose there are three such alleles, with frequencies 1/4, 1/4, and 1/2. What is the probability of a trichromatic female?

  4. [25 Points] 2000 Gametes from an AaBbCc individual are scored, with the following numbers seen:

    ABC 0aBC 28
    ABc 17aBc 945
    AbC 955abC 23
    Abc 32abc 0

  5. [5 Points] Why is it the case that human males are more likely to be deficient in either red or green color vision rather than blue color vision?

  6. [5 Points] Contrast chromosomal sex determination in flies with that in humans.

  7. [5 Points] Give two different mechanisms (and an example of a species in which each occurs) in which dosage compensation is achieved.

  8. [5 Points] Define both Penetrance and expressivity .

  9. [5 Points] Looking at paired chromosomes in meiosis, how would one distinguish between an individuals heterozygous for an inversion and an individual heterozygous for a translocation? You can use a drawing, if you wish.

  10. [20 Points] Consider the following three coat-color genes, which have the following phenotypes: D- = full color; dd = dilute color; A-B- = Gray, A-bb = Black, aaB- = brown, aabb = cinnamon. D is unlinked to A and B, while A and B are linked at recombination frequency c=0.2. What are the expected frequencies of the eight possible coat phenotypes in the offspring of a cross of ABD/abd to abd/abd ?

  11. [5 Points] The following 3 (unordered) octads types are seen on an AaBb parent:

    Type 1 (AB, AB, AB, AB, ab, ab, ab, ab) Frequency = 56%
    Type 2 2 (AB, AB, ab, ab, Ab, Ab, aB, aB) Frequency = 26%
    Type 3 2 (Ab, Ab, Ab, Ab, aB, aB, aB, aB) Frequency = 18%

    What is the A-B recombination frequency?

  12. [5 Points] In a study to estimate mutation rate, 1000 flasks, each containing 107 cells are examined. If 125 of the flasks are mutant-free, what is the estimated mutation rate?