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Genetics L311 final exam
December 16, 2016
Directions: Please read each question carefully. Answer questions as concisely as possible. Excessively long answers, particularly if they include any inaccuracies, may result in deduction of points. You may use the back of the pages as work sheets, but please write your answer in the space allotted. However, you must show all your work. Clearly define your genetic symbols. We will not make guesses as to what a particular symbol is intended to mean. Also, don’t assume that strains are true-breeding unless this is stated in the question. Finally, show all your work. Good luck.
page 2 (30 points possible)
page 3 (24 points possible)
page 4 (33 points possible)
page 5 (24 points possible)
page 6 (25 points possible)
page 7 (22 points possible)
page 8 (18 points possible)
page 9 (24 points possible)
total (of 200 points possible)
1. Short answers (2 pts each, for total of 30 pts)
A. The collective genetic information present among all members of a population is referred to as the .
B. A distinct breeding group within a larger interbreeding group of individuals is referred to as a(n) .
C. During , the number of mobile DNA elements within the cell remains constant.
D. The tendency of two genes located on the same chromosome to co-segregate is called .
E. A protein that specifies different fates depending on its level is a(n) .
F. (H2) provides an estimate of the genetic contribution to a trait.
G. is when mutation of a single gene produces multiple phenotypes.
H. Many familial cancer syndromes are cell recessive but transmit as autosomal dominant. The explanation for this phenomenon is that in one or more cells, wild type gene function is lost. This occurs most commonly through the phenomenon of , where the chromosome, or a portion of the chromosome with the wild type gene is lost.
I. Activation of a cell death program involves activation of cellular proteases called .
J. A plant or animal with four sets of chromosomes, regardless of their origin, is said to be .
K. The provides a measure of variation, including both genetic and environmental factors.
L. A mutation in which the gene acquires some new activity is called a mutation.
Please provide a brief definition of each of the following:
M. dosage compensation:
N. allele:
O. linkage equilibrium:
2. Phenylketonuria (PKU) is an autosomal recessive disorder that affects about 1 in 18,000 in North America. Untreated it can cause mousy body odor, pale skin and most significantly, mental retardation. Fortunately, if detected soon after birth babies placed on a low phenylalanine diet generally avoid all of these symptoms. For this reason, newborns are routinely screened for PKU. Assume that this population meets Hardy-Weinberg criteria.
A. What are the frequencies of the mutant and wild type alleles (6 points)?
B. What is the frequency of heterozygous carriers in this population (4 points)?
C. A couple from this population seeks advice from their genetic counselor. With a previous husband, the woman had a child with PKU. The two men are unrelated to each other and her current spouse does not have any family history of PKU. What is the risk that their first child will have the disease (6 pts)?
3. Below is a signaling pathway that regulates wing development in Drosophila, among many other things. For the purposes of this question we will ignore any other functions of this signaling pathway.
wnt frz gsk3 cat tcf wing
What phenotypes do you expect mutations in the following to produce? Note: All mutations are loss-of-function (8 points).
wnt
gsk3
tcf
gsk3; tcf
4. The exotic sea squirt N. rajovicae is diploid with two pairs of chromosomes, one long and one short. Mutations in the orn gene cause animals to develop orange coloration, mutations in opq causes them to be opaque rather than transparent and mutations in ssp cause them to siphon water at an unusually high rate. A particular individual, named Nikola, is heterozygous for orn and opq, and homozygous mutant for ssp. You demonstrate that the orn and opq mutant alleles are in the trans configuration. ssp is located on the short chromosome not linked to orn or opq.
A. Please show one of Nikola’s cells in prophase of mitosis. Please include the alleles of each gene. Draw a circle around one pair of homologs and a square around one pair of sister chromatids (6 points).
B. Occasionally meiosis goes awry. Please show the products of meiosis where nondisjunction of the long chromosome has occurred during meiosis I. You do not need to show the genes (10 pts).
5. You discover two unusual true-breeding strains of the iridescent tropical squirrel, E. qinae. Both have pale blue fur. A cross of true-breeding strain 1 X true-breeding strain 2 produces all dark blue offspring. A cross of dark blue F1 X dark blue F1 produces the following:
453 dark blue
301 pale blue
49 white
A. Please give the genotypes of the F2’s on the lines provided above (12 points).
B. What is the probability that if you choose a pale blue-furred squirrel at random, it would be homozygous for all of the genes (5 points)?
6. Drosophila anterior-posterior body axis is patterned by a series of sequentially acting classes of genes. A. Please provide the names and function of each class of gene, the order in which they act, and provide an example of one gene in each class (10 points).
B. You find a mutation in a gene that you call antenna-leg, in which the animal has antennae growing where legs should be. What class of genes is antenna-leg likely to belong to (4 points)?
7. In C. elegans, cell-cell signaling specifies vulval cell fates, causing the Pn.p cells to adopt primary, secondary or tertiary fates. Give the predicted effect of the following mutations in each of the cell fates listed (i.e. increase, decrease or no change, 2 pts each, 10 pts total):
primary rationale
A. loss of EGFR (let-23)
B. gain-of-function mpk-1 (kinase
downstream of Ras)
C. loss of EGF plus
activating mutation in Ras
D. transcription factors (lin-1 or lin-31)
that can’t be inactivated
E. loss of transcription factors
plus loss of Ras
8. Robinow Syndrome is found in different forms, which show different modes of transmission. The pedigree below shows the transmission of one form of the disease. Affected individuals show the trait from birth.
A. What mode of inheritance does this form of Robinow Syndrome show (4 points)?
B. Obligate carriers are individuals who must carry the mutation that produces the trait. Please list the obligate carriers in the pedigree at right (4 points).
C. What is the probability that II-3 carries the mutation (i.e. is heterozygous, 3 points)?
D. What is the probability that IV-2 and IV-3’s next child will be a boy who is affected by the disease (3 points)?
9. The rare jungle millipede, A. schlenzae, has been found in two true breeding strains. Strain A is white and has short legs, while Strain B is red and has long legs. A cross of Strain A males and Strain B females results in offspring that all have red shells and long legs. Crossing the F1 animals results in the following:
603 red, long legged females
298 red, long legged males
302 white, long legged males
201 red, short legged females
99 red, short legged males
97 white, short legged males
A. Fill in the genotypes of the F2 progeny (6 points).
B. What do you expect from a cross of red, long legged female F1 X white, short legged F2 males? Please provide the phenotypes and relative frequencies (5 points).
10. Progression through the cell cycle is tightly regulated. In particular, we looked at how the cell regulates entry into S phase.
A. Please illustrate the steps involved in a cell’s decision to enter S phase. Include the relevant proteins. You may use a diagram if you wish (5 points).
B. Cells use several different checkpoints to verify that essential steps are completed before proceeding to the next event during the cell cycle. Please show how the cell arrests in the cell cycle prior to entry into S phase if DNA damage is detected. Include the relevant proteins (5 points).
C. Using the genes discussed in lecture, first determine whether the following mutations would increase, decrease, or not change the probability of cancer. Please briefly state your rationale. lf = loss of function, gf = gain of function (think of this as resulting in continuously active gene product independent of upstream inputs, 12 points).
Mutation Probability Rationale
Rb (lf)
Ras (gf)
Deletion of erbB inhibitory
domain
Ras (lf) plus loss of
erbB inhibitory domain
11A. We looked at the genetic pathway that determines gender in C. elegans. The pathways is shown below. What phenotype would we expect to see result from the following mutations (6 points)?
if X:A=0.5 if X:A=1.0
xol-1(gf)
loss of tra-2
tra-1 (gf) and loss of
fem-2
B. 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 (4 points).
12. When traveling in a cave near Bloomington, you came across a species of bat, A. farlowae. Two recessive mutations are known, one causing glow-in-the-dark wings (g) and the other causing hairy feet (h). When trying to create a monster bat for a reality TV show, you cross heterozygous parents, both with the mutations in trans, hoping to produce bats with hairy feet and glowing wings. Since the mutations are only 4 mu apart you assume no double crossovers. What percentage of offspring will have glowing wings and hairy feet (8 points)?
13. In your studies of the unusual flying fish species B. kochae you find two strains. Strain 1 has light blue scales and long fins. The second strain has purple scales and short fins. A cross of strain 1 females with strain 2 males produces F1 that all have lavender scales. Half of the F1’s have long fins and half have short fins. You cross the lavender scaled, short finned F1s and find:
1/12 purple scales, long fins
1/6 lavender scales, long fins
1/12 light blue scales, long fins
1/6 purple scales, short fins
1/3 lavender scales, short fins
1/6 light blue scales, short fins
A. Please give the genotypes of the F2s on the lines above (12 points).
B. Purple scale, short finned F2 X light blue scaled, long finned F2. What fraction of the offspring will have lavender scales and short fins (4 points)?
C. In another group of the same species of fish you find mutants that produce yellow spots rather than the usual orange. When you cross true-breeding yellow females with true-breeding orange males, the progeny all have yellow spots. When you cross these the next generation all have orange spots. How can you explain this result? Please name the mode of inheritance spot color displays (8 points).
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