name:______
student ID:______
Genetics L311 exam 3
November 13, 2015
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 ______(20 points possible)
page 3 ______(22 points possible)
page 4 ______(28 points possible)
page 5 ______(16 points possible)
page 6 ______(14 points possible)
total ______(of 100 points possible)
1. Short answers (2 points each, 20 points total)
A. Spontaneous mutations are mutations that arise in the absence of any obvious inducing agents.
B. Phage that grow only via a lytic life cycle are said to be virulent.
C. Naturally occuring Xenopus laevis have 4 sets of chromosomes that appear to be derived from two different species. If true, then Xenopus is an example of allotetraploidy or allpolyploidy.
D. The exchange of DNA between bacterial cells, called conjugation, involves direct contact between participating cells.
E. A bacterial cell that is diploid for a portion of its genome is referred to as merodiploid.
F. An individual with only one copy of each of the chromosomes in the organism is said to be monoploid (not haploid). Such individuals are usually sterile.
G. Chromosomal walk or positional cloning is the general method of cloning a gene by taking advantage of what’s known about its chromosomal location and the presence of a nearby cloned gene.
Please provide concise definitions of the following terms:
H. lysogeny: Integration of a bacteriophage genome into a host cell’s genome.
I. gene therapy: Correcting a genetic defect by providing the wild type copy of the relevant gene.
J. holocentric: A chromosome in which the centromere extends along the length of the chromosome.
2. You wish to use deletion mapping with polytene chromosomes. If the genes are positioned as shown, please indicate the expected outcomes of a cross of each deletion X homozygous mutant flies. In other words, in the first square in the table use a + to indicate that the offspring of a cross of Deletion 1 X a-/a- will be phenotypically wild type and a – to indicate that they will be mutant, etc (10 points).
3. In studying a particular animal, you find that some of the chromosomes appear a bit unusual. The relevant chromsomes are shown below. One pair of homologues is on the left and the second pair is shown on the right. For each pair, the normal chromosome is the one on top.
A. What is the name of the chromosomal alteration that generated the abnormal chromosomes (2 points)? Reciprocal translocation
B. Show the chromosomes synapsed in meiosis. Please include the genes (5 points).
C. You find an individual homozygous for the abnormal chromosomes as shown below. Show this individual's chromosomes synapsed in meiosis. Please include the genes (5 points).
The chromosomes will appear as drawn above.
4. The human gene, tkc, causes affected individuals to uncontrollably crave turkey. You have cloned the human tkc gene. To study tkc further, you want to molecularly clone the gene from mice. You have designed primers based on the sequence of the human gene, and you show experimentally that those same primers produce a single, specific PCR product with mouse DNA.
A. Please describe how you would go about cloning the mouse tkc gene (8 points).
Isolate mouse genomic DNA or prepare cDNA
Cut DNA and vector with restriction endonuclease
Ligate
Transform bacteria
Select for colonies
Colony lift (see lecture notes for steps) using PCR product generated using mouse DNA as template.)
B. To understand the function of tkc in mice, after cloning the gene you decide to generate mice lacking the gene. Explain how you would generate such mice. Please include a diagram of the vector including all relevant features (8 points).
Infect ES cells from black mouse with vector.
Select on neo and gan.
Verify deletion by Southern or PCR.
Introduce into embryo from white mouse and implant in suitable host.
Identify chimeric mice.
Cross with white mouse, identify black furred offspring.
Determine which black furred offspring have tkc knocked out.
Cross hets to get homozygotes
C. To further understand tkc function you want to determine what tissue types express the gene. Briefly describe and name the general strategy that you would use to accomplish this. You do not need to provide the steps involved. A one or two sentence answer should be sufficient (4 points). Make a reporter transgene in which you’ve fused tkc (either coding plus promoter or just promoter) to some detectable gene product such as lacZ, gfp or luciferase gene
5. Your pet pig Porky is the smartest and friendliest pet on the block. She also has a rare zebra-striped skin pattern. Porky attracts a lot of attention during your frequent walks with her in the park. You come to believe that you could make a lot of money selling Porky clones on eBay. How would you go about cloning Porky (8 points)?
Obtain an egg from a pig
Remove its nucleus
Fuse the enucleated egg to a somatic cell from Porky
Implant the embryo into a host female to permit development to term.
6. As a member of a deep-sea marine expedition, you discovered a new species of sea cucumber, A. farlowae, several years ago. On a recent trip you find two strains of A. farlowae that differ in skin color. A single gene specifies skin color. You perform the following crosses and obtain the surprising results shown.
Cross true-breeding orange female X true-breeding blue male => orange F1s
Orange F1 female X orange F1 male => all blue offspring
Cross blue F2 female X blue F2 male => 1/4 orange and 3/4 blue offspring
A. How do you explain this result (5 points)?
The genotype of mom seems to determine the phenotype of the offspring. Blue appears to be dominant over orange.
B. Please provide the genotype(s) of the blue F2 animals (3 points)?
b+/b+, b+/b– and b–/b–
C. What name do we give to the mode of inheritance shown in this question (2 points)?
maternal effect
7. There has been a great deal of interest in the potential for use of stem cells to treat a variety of disorders.
A. Please name the three general types of stem cells and list an advantage and a disadvantage of each (6 points).
Advantages / DisadvantagesEmbryonic stem cells / Pluripotent
Indefinite proliferation / Organ rejection
Controversial
Adult stem cells / Organ rejection less likely
Don’t destroy human embryo / Not pluripotent
Limited proliferation
Induced pluripotent stem cells / Pluripotent
Indefinite proliferation Organ rejection less likely Don’t destroy human embryo / Possible increased risk of tumor formation
8. In an interrupted mating mapping experiment, you obtain the results shown in the graph below. The experiment was conducted as described in class.
A. Show the genetic map for each of these genes on the circular chromosome. Indicate the location of the origin and the direction of transfer. Doesn’t need to be drawn to scale (6 points).
B. What are the genotypes of the donor and recipient strains (4 points)?
donor: Hfr trp+ met+ leu+ arg+ lys+ strS
recipient: F– trp– met– leu– arg– lys– strR
C. For each gene, the number of recombinants increases with time until they reach a maximum. Why does the number of recombinants for a given gene increase with time (2 points)?
Matings are not synchronous.
D. Why does the number or recombinants reach a maximum (2 points)?
The probability of sepration equals the probability of new matings being initiated.
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