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Name_____________________
Genetics C3032 - Examination #1 - October 6, 2005
General instructions: Don't Panic. Be sure your name is on every page. Answer the questions in the
space provided. Clearly state your reasoning; if we understand what you are saying during the grading,
you will have a better chance of getting at least partial credit. The value of each question is indicated.
1. (32 points - 8 each) How would you do the following? Be succinct, but be sure to say what the outcome
of the experiment you do will be.
a. Distinguish between a drug that interfered with ligase=s action in DNA replication and one that
interfered with DNA polymerase I=s action.
b. Demonstrate that a mutation results in nondisjunction of the X chromosome in C. elegans.
c. Determine whether a DNA virus was in a drop of blood found at a crime scene (this would be far too
little sample to run on a gel).
d. Given wild-types and animals with a recessive, sex-linked mutation, determine whether the animals
used an XX/XY (or XX/XO) system or a ZW/ZZ system.
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Name_____________________
2. (24 points - 8 each) For each of the following you mate the indicated true breeding Drosophila strains
and then mate the resulting F1 progeny together. For each set (i) explain how the ratio of phenotypes
occurs (a demonstration with a Punnett Square would be useful) and (ii) give the phenotypes and
genotypes of the F1 animals that were mated together.
a. Strains A and B: The F2 progeny have phenotypes in the ratio of 9A:3AB:3WT:1B.
b. Strains C and D: The living F2 progeny have phenotypes in the ratio of 9C:3WT:1D.
c. Strain E females and Strain F males: 2E females:1E males:1F males
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3. (24 points) A very large mutagenesis in C. elegans with the chemical ethyl methanesulfonate (EMS)
identified >50 mutations affecting the α-helical tail of the muscle
U
C
A
G
2nd →
protein myosin. (Assume that EMS only causes GC to AT
3rd 1st
changes for this problem.) When the mutant alleles were
U U
F
S
Y
C
sequenced, all of the mutations were nonsense mutations (i.e.,
C
F
S
Y
C
A
L
S
Ochre
Opal
no missense mutations were found). This result was quite
G
L
S
Amber
W
unexpected and you are asked to evaluate the data.
a. (4) What type of change is the GC to AT alteration caused by
EMS?
U
C
A
G
C
L
L
L
L
P
P
P
P
H
H
Q
Q
R
R
R
R
U
C
A
G
A
I
I
I
M
T
T
T
T
N
N
K
K
S
S
R
R
U G
C
A
G
V
V
V
V
A
A
A
A
D
D
E
E
G
G
G
G
b. (8) The introduction of a glycine or a proline should disrupt
the α-helix and cause a mutant phenotype (genes synthesized
in a separate experiment with these mutations do not act like the wild type). Why were no mutations of
this type seen?
c. (4) How can a single nucleotide change caused by EMS cause nonsense mutations? Give one
example and be sure to give the change in the DNA.
d. (4) Can a single nucleotide change caused by EMS cause missense mutations? If not, explain why. If
so, give an example (be sure to give the change in the DNA).
d. (4) Why do you suppose that only nonsense mutations but no missense mutations were seen? In other
words, what can you deduce about the importance of the amino acids in the α-helix for its functions?
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Name_____________________
4. (20 points - 4 points each) Answer TRUE or FALSE. If the statement is TRUE, explain or give a
supporting example. If the statement is FALSE, either correct the statement or give a counterexample.
a. A wild type phenotype is the one that is most commonly found in a population.
b. Incomplete penetrance leads to a lower percentage of animals showing the mutant phenotype than
expected.
c. Mutant phenotypes only arise from changes in the sequence of the DNA.
d. A major consideration in the establishment of model systems for genetic studies is the ease at which
they can be grown in a laboratory setting.
e. The greater appearance of mutant phenotypes when a population inbreeds is due to a change of
mutation rate.