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Spring 2005
BIOL 212 Genetics
Exam II
Please read all questions carefully and show your work for complete credit.
The exam is worth 80 points. Please put your name and lab section on both the
SCANTRON and the exam. A genetic code table is available on the last page of the
exam.
Part I. Multiple choice (3 pts. each). Select the one best answer for questions 1-21 and
use a #2 pencil to complete the SCANTRON provided.
1. Genes A, B, and C are linked. Crossover gametes between A and B are recovered 15%
of the time and crossovers between B and C 10% of the time. What percentage of double
crossovers is expected among A, B, and C?
a. 25%
b. 15%
c. 5%
d. 1.5%
2.
a.
b.
c.
d.
The strand of DNA that is replicated in short pieces, later joined together, is the
replication fork
leading strand
lagging strand
template strand
3. Which of the following strains is a prototroph?
a. thr+ leu- met+
b. thr- leu+ metc. thr- leu+ met+
d. thr+ leu+ met+
4. If in Griffith's experiment, a mixture of heat-killed smooth bacteria and living rough
bacteria were injected into a mouse, it would be expected to __________.
a. kill the mouse
b. cause transfection
c. cause transduction
d. have no effect on it
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5. The mutations cinnabar (cn, bright red eyes) and vestigial (vg, reduced wings) are
linked on the second chromosome of Drosophila. Among 1000 progeny of the cross of
cn +/+ vg females and cn vg/cn vg males, the following genotypes were observed:
cn vg/cn vg
cn +/cn vg
+ vg/cn vg
+ +/cn vg
35
455
465
45
The recombination frequency between cn and vg is
a. 8%
b. 16%
c. 46%
d. 92%
6. Which cluster of terms accurately reflects the nature of DNA replication in
prokaryotes?
a. fixed origin, bidirectional, conservative
b. fixed origin, unidirectional, conservative
c. random origin, bidirectional, semiconservative
d. fixed origin, bidirectional, semiconservative
7. The difference between a ribose and a deoxyribose sugar is:
a. The hydroxyl group at the 3' carbon of the sugar.
b. The phosphate group at the 3' carbon of the sugar.
c. The hydroxyl group at the 2' carbon of the sugar.
d. The phosphate group at the 5' carbon of the sugar.
8.
a.
b.
c.
d.
Specialized transduction differs from generalized transduction because
only one or two genes are transferred by specialized transduction
any bacterial gene can be transferred by specialized transduction
only lytic phage mediate specialized transduction
an F plasmid is involved in gene transfer in generalized transduction
9. A protein fragment has the following sequence: NH2-Met-His-Glu-Ala-Trp-COOH.
A possible mRNA carrying the information for this protein is:
a. 5'AUGCACGAAGCUUGG3'
b. 3'AUGCACGAAGCUUGG5'
c. 5'AUGCAUGAGUUUUGG3'
d. 5'CCAAGCUUCGUGCAU3'
2
10. Insertion of a single base in a DNA sequence results in what kind of mutation?
a. Deletion
b. Frameshift mutation
c. Point mutation
d. Transition
11. The growing polypeptide chain in the ribosome during translation is attached to the
__.
a. ribosome small subunit
b. 3' end of the mRNA
c. 3' end of a tRNA
d. initiation factor
12. Conjugation involves all of the following except __________.
a. sex pilus
b. bacterial contact
c. fertility factor
d. transformation
13. Below is a table which presents the effect of different media on the growth response
of tryptophan mutations in the bacterium Salmonella typhimurium (+ = growth, - = no
growth)
Medium Supplemented with
Strain
No Supplement IGP
AA
IN
TRP
trp-8
+
+
+
+
trp-2
+
+
+
trp-3
+
+
trp-1
+
The biochemical pathway for the compounds IGP, AA, IN, and TRP based on these data
is
a.  IGP  AA  IN  TRP
b.  AA  IGP  IN  TRP
c.  TRP  IN  IGP  AA
d.  AA  IN  IGP  TRP
14. E. coli DNA polymerase I has an essential function in DNA replication. Which of
the following is that function?
a. filling in gaps when introns are removed
b. separating the two strands of double stranded DNA
c. extending RNA primers as the main E. coli replication enzyme
d. removing RNA primers and filling in gaps in the DNA
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15. Translation of mRNA in a ribosome proceeds __.
a. from the middle simultaneously toward the 3' and 5' ends
b. from either the 5' or 3' end, depending on the enzymes present
c. from the 5' end to the 3' end
d. from the 3' end to the 5' end
16. Most inborn disorders of metabolism associated with the phenylalanine - tyrosine
pathway have deleterious effects because:
a. necessary metabolic end products are not synthesized
b. the defective enzyme responsible for the block accumulates to toxic levels
c. intermediate compounds that are not metabolized at the blocks accumulate to toxic
levels
d. cells cannot obtain enough energy to function normally
17. Two bacterial strains were obtained with the following genotypes:
Hfr: ala+leu+thi+strs (alanine and leucine are amino acids, thiamine is a vitamin)
F-: ala-leu-thi-strr
After conjugation, you want to select F- recombinants that are ala+leu+thi+. Which of the
following media would you use for this selection?
a. rich medium containing streptomycin
b. minimal medium containing streptomycin
c. minimal medium containing thiamine
d. minimal medium containing alanine, leucine, thiamine
18. In a translation assay with a repeating copolymer (AUAU…), what would you expect
to happen?
a. Isoleucine (ile) will be incorporated into the protein.
b. Tyrosine (tyr) will be incorporated into the protein.
c. Isoleucine and tyrosine will both be incorporated into the protein.
d. There will be no protein incorporation.
19. Which of the following does NOT happen during hnRNA processing?
a. A 7-methylguanosine cap is added to the 5' end of the RNA.
b. Introns are spliced out.
c. A poly A tail is added.
d. Ribosomes bind and begin translation.
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20. Two Hfr strains, A and B, are derived from a single F+ strain of E. coli. The
following chart shows the entry times of the first five markers into an F- strain when each
is used in an interrupted mating experiment:
HfrA
HfrB
d+ (3)
e+ (29)
c+ (32)
b+ (37)
a+ (47)
g+ (7)
h+ (17)
d+ (23)
e+ (49)
c+ (52)
Assume a 100 min. circular map. A correct order for the genes and F factors (shown by
brackets) is
a.
b.
c.
d.
b+a+[B]g+h+[A]d+e+c+
b+c+e+d+[A]a+[B]g+h+
b+a+[A]g+h+[B]d+e+c+
g+h+[A]d+e+c+[B]a+b+
21. (Bonus question) In Drosophila, the two genes w (white) and sn (singed) are Xlinked and 25 map units apart. A female fly of genotype w+sn+/wsn is crossed to a male
from a true-breeding wild type line. What percent of male progeny will be singed?
a. 0
b. 12.5
c. 25
d. 37.5
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Part II: Problems. Answer these questions in the space provided below.
22. Problem: Show your work for full credit (12 pts.)
In corn, three linked recessive traits are symbolized b, c and d; the corresponding wild
type alleles are indicated by +. A cross between two true-breeding plants ++d/++d and
bc+/bc+ gives all heterozygous plants, ++d/bc+. A testcross of the F1 heterozygotes gave
the following F2 phenotypes:
phenotypes
b++
+cd
++d
bc+
b+d
+c+
bcd
+++
#observed
100
88
340
360
46
48
8
10
total 1000
a. Calculate the recombination frequencies between genes b, c and d. Show your work.
b. Construct a linkage map of the three genes.
c. Show the best estimate of the distance between the two most distant markers.
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23. (8 pts.) Assume that you grew a culture of E. coli for many generations in medium
containing ammonium ion labeled with 15N, a heavy isotope of nitrogen. You then
transfer the cell to medium containing the lighter isotope 14N for two successive
generations. Using different symbols for old 15N and new 14N DNA strands ( | = 15N and
: = 14N), show the DNA strands you predict would be produced
(a) assuming the semiconservative model of replication
generation 0
||
generation 1
generation 2
(b) assuming the conservative model of DNA replication
generation 0
||
generation 1
generation 2
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Genetic code table
8