Problem Set 13, Fall 2015
8 points total
Name:
1. What phenotypes do you expect to result from mutations in the following genes?
A. in C. elegans:
if X:A=0.5
if X:A=1.0
fem-3
xol-1
sdc-2
B. in Drosophila:
tra
dsx
2. You identified a mutation in the Drosophila gender identity crisis (gic) gene. You find the
following results in genetic crosses:
gic-/gic- female X gic-/gic- male
99.9% female
A. Give two plausible explanations for this result.
B. How would you distinguish between these two possibilities?
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Problem Set 13, Fall 2015
8 points total
Name:
3. What phenoytpes do you expect to result from mutations in the following genes?
A. In C. elegans :
if X:A=0.5
if X:A=1.0
fem-2
her-1
tra-1
B. J. mannae are found in two general moods, either happy or cranky. Surprisingly you find that
mood in J. mannae is under the control of a simple genetic pathway. Careful genetic analysis has
defined the genes involved in control of disposition. The pathway is shown below. Arrows and
bars indicated positive and negative regulatory interactions, as used in lecture.
What disposition do you expect for loss of function mutations in:
gen1
gen2
gen4
4. An extremely rare genetic disorder leads to great success in L311. You find the pattern of
inheritance displayed in the pedigree below. A. What mode of inheritance does this trait display?
B. Explain the mechanism of this mode of
inheritance.
C. If the individuals labeled a, b, c, d, e, f
were all unaffected, what mode of inheritance would be displayed.
D. Explain the general mechanism of the mode of inheritance expected if the pattern in part C
were exhibited.
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Problem Set 13, Fall 2015
8 points total
Name:
5. Mutations in many genes are associated with a variety of cancers. Some mutations may be
expected to increase the probability of developing cancer, whereas others might reduce the
probability. Based on what you know about their roles, do you expect the following mutations to
increase, decrease or cause no change to the probability of developing cancer? Provide a brief
rationale for each of your answers.
mutations that:
eliminate E2F
likelihood of
developing cancer
rationale
eliminate p53
eliminate bcl-2 function
activate Ras
eliminate p53 and
activate Ras in same cell
6. Two strains of S. myersae are known. One has short hair and one has long hair. You cross true
breeding short-haired females X true breeding long-haired males and get all short-haired F1
progeny. You cross F1 short-haired females X F1 short-haired males and get all long-haired F2
progeny.
A. Explain why the F2’s are all long-haired whereas the F1’s all had short hair.
B. What mode of inheritance does this represent?
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Problem Set 13, Fall 2015
8 points total
Name:
7. A cross between a purebred black mouse and a purebred white mouse yields all black F1
offspring. These black F1 mice are crossed to produce an F2 generation. You observe the
following F2 phenotypic ratio:
White: 22
Black: 175
Gray: 114
A. Draw out the crosses described above, showing the genotypes of the parents, F1 and F2.
B. What is the simplified ratio illustrated in this cross?
C. You cross white mice from the F2 generation X black mice from the F2 generation. What is
the probability of getting black offspring from this cross?
8. Dosage compensation in Drosophila and C. elegans is implemented after sex determination
has occurred in the developing embryo. Why must this be true? Please explain in the context of
what you know about these processes during Drosophila development.
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