Final Exam Genetics 408/508-(2000)
Question # points points earned
1
5.5
2
6.0
3
6.0
4
6.5
5
6.0
TOTAL
Name
ID
30.0
1. (5.5 points) DNA nucleases play prominent roles in DNA replication, recombination and
repair. Name one nuclease that functions in each of these processes and briefly describe its
specific function. Also indicate what happens if the helicase you have indicated is not present in
the cell (null mutation).
REPLICATION
RECOMBINATION
REPAIR
1
Name
ID
2. (6 points) Answer the following questions. Explain your answers fully. Focus your answers
to the specific questions, but I want to see how much you know about this subject. So, include
relevant information from both genetic and biochemical experiments. Illustrations may be
useful.
a. (3 points) Describe the consequences of DNA Pol I deficiency plus RecA deficiency (the
polA recA double mutant) in a bacterial cell.
b. (3 points) Describe the consequences of exonucleolytic proofreading deficiency for DNA pol
δ plus msh2 deficiency (MMR deficiency) in a yeast cell.
2
Name
ID
3. (6 points) How do DNA repair enzymes find DNA damage? Describe potential obstacles and
describe at least three strategies used by cells to overcome these obstacles.
Obstacles:
1.
2.
3.
3
Name
ID
4. The “Ames” test provides a way to identify mutagens. This test measures reversion of
certain mutations in the histidine operon of Salmonella. The tester his alleles revert by
different mutational events.
(1 point) Describe the types of possible mutational events required to revert a nonsense
codon (translation termination codon). The nonsense (or amber) codon is indicated in large
bold letters and is underlined.
amber his-
5' …C A G T A G T A T…
3' …G T C A T C A T A…
(2 points) Describe two different mechanisms in which the indicated mutations can be
produced in the cell.
1)
2)
(1 points) Describe possible mutational events required to revert the following frameshift
mutation (fs). Codons are underlined.
wt:
5' …G C A A A A A A A T T C …
3' …C G T T T T T T T A A G …
fs his-:
5' …G C A A A A A A A A T T C …
3' …C G T T T T T T T A A A G …
4
Name
ID
Question 4 continued.
The two Salmonella tester strains were exposed to a chemical that may have the potential to
damage DNA. Only a small increase in His + revertants was detected for the two tester strains
(Fig. 1). However, when the tester strains were transformed with a plasmid carrying genes
called mucA and mucB, the chemical caused a high amount of His + revertants for the amber
his- strain, but not for the fs his- strain (Fig. 1).
mucA,B plasmid, amber his-
2000
His+
1000
20
40
60
80
Chemical dose (ng)
amber hismucA,B plasmid, fs hisfs his100
(2.5 points) Propose one mechanism to explain how the mucA,B genes increase the sensitivity to
the amber his- strain to the chemical. Explain why the reversion frequency of the fs his- strain
does not increase by addition of the mucA,B genes.
5
Name
ID
5. ( 6 points) Discuss the current view of the mechanism of aging. Use experimental evidence
to support this mechanism.
6