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ANSWERS TO Exam Questions from Final Exam – Human Genetics, Nondisjunction, and
Cancer, and Cumulative Questions
1. You are working on two different organisms -- the fruit fly Drosophila and the yeast
S. cerevisiae
(a) how to make this strain in yeast: mate C haploid mutants to E haploid mutants.
how to make this strain in Drosophila: mate true-breeding C mutants to true-breeding E
mutants
list all of the possible genetic tests for which this strain could be used:
complementation, dominant/recessive, trans
(b) how to make this strain in yeast: mate C mutant haploids to D mutant haploids,
induce sporulation of the diploids, look for NPD tetrads (4 spores, 2 normal, 2 double
mutant)
how to make this strain in Drosophila: can’t be made, flies are diploid
list all of the possible genetic tests for which this strain could be used: epistasis
(c) complementation, dominant/recessive, cis, trans
2. On the next page is a pedigree showing a couple that has a child with trisomy of
chromosome 21.
(a)
maternally inherited
allele(s) at SSR 53
C B
paternally inherited
allele(s) at SSR 53
BB B
maternally inherited
allele(s) at SSR 78
F F
paternally inherited
allele(s) at SSR 78
FF E
maternally inherited
allele(s) at SSR 99
I I
paternally inherited
allele(s) at SSR 99
HJ H
(b) Father (individual 1):
H
F
B
J
E
B
Mother (individual 2):
(c) Individual 3
(d) the dad (individual 1)
(e) meiosis I
(f)
i) the cell in metaphase I
ii) the two cells in metaphase II
J
E
B
J
E
B
H
F
B
H F B J E B
J
F
B
H
E
B
H
F
B
I
F
C
K
F
B
(d) cI sm1 sm
5. A ship carrying 7,000 passengers is about to land on an island that has 33,
occupants.
(a) q =(21/3500) = 0.
(b) 2pq = 0.
(c) q = 0.
(d) (1/2)q = 0.
Genotype of strain Will cheX be expressed
when chemoattractants
are absent?
Will cheX be expressed
when chemoattractants
are present?
wild-type No Yes
cheC1 Yes Yes
cheB2 / F’ P
X
cheX+
Yes Yes
cheA3 / F’ cheC1 No No
cheX+ cheB2 cheA3 No No
P
X
cheX+
/ F’ cheC1 P
X
cheX+
No Yes
7. You are studying cancer progression in mice.
(a) constitutive
(b) recessive
(c) tumor suppressor
(d) to inhibit cell division whenever nutrients are absent
(e) constitutive
(f) dominant
(g) proto-oncogene
(h) to promote cell division whenever nutrients are present.
(i) yes because of loss of heterozygosity
(j) one wild-type allele
(k) two mutant alleles
8. You are mapping a certain rare disorder that is caused by an allele at the N locus.
maternally inherited
allele at SSR
C A A A C C A
paternally inherited
allele at SSR
B C C B B C B
maternally inherited
allele at the N locus
n n n n n n n
paternally inherited
allele at the N locus
N n N N N n n
maternally inherited
allele at the N locus
n N n n n N N
paternally inherited
allele at the N locus
n n n n n n n
(a) father – individual one
(b)
(c) mother – individual two
IF the condition is
autosomal
dominant
[parts (c) - (e) ]
(Individual 2 is “Nn”)
IF the condition is
autosomal
recessive
[parts (a) and (b) ]
(Individual 2 is “nn”)
C
n
B
N
12. The cI gene of phage lambda encodes a repressor protein that has a molecular
weight of 24 kDa.
(a) an amber nonsense mutation 2/3 of the way into the coding region
(b) a +1 or –1 frameshift mutation that lies shortly before the nonsense mutation
(c) 5’-TGG-3’
(d) 5’-TAG-3’
13. Your colleague, who is a medical geneticist, seeks your help in interpreting a
patient: an XXY girl.
(a) mother
(b) meiosis II
(c)
i) the cell in metaphase I
ii) the two cells in metaphase II
1A
2A
3B
4B
1A
2A
3B
4B
1C
2B
3A
4C
1C
2B
3A
4C
1A
2A
3B
4B
1A
2B
3A
4B
1C
2A
3B
4C
1C
2B
3A
4C
iii) the four final products of the meiosis
(d) a translocation during the development of the sperm in the father, so that the Sry
gene went to the X chromosome, and SSR1 went to the Y chromosome
14. Your colleague seeks your advice regarding a family in which several individuals
(filled circles or squares below) developed colon cancer in their 30's or 40's.
(a) if you see SSR instability in the tumor cells, then it is most likely HNPCC
(b) log (0.5)
7 = 2.
7
(c) yes, it becomes:
log (0.5)
6
= 1.
6
(d) yes
(e) no, child #2 is a recombinant
(f) yes
15. Wild-type E. coli bacteria are motile (that is, they can swim around).
(a) 70%
(b) unlinked (more than 100kb away)
(c)
Tn 3 1
1A
2B
3A
4B
1C
2B
3A
4C
1A
2A
3B
4B
1C
2A
3B
4C
19. HNPCC (Hereditary Non-Polyposis Colon Cancer) shows autosomal dominant
inheritance in humans.
(a) knockout of the mouse MSH2 gene
(b) more quickly
20. Your project is to genetically map the locus for color blindness, an X-linked
recessive trait, with respect to SSR markers.
(a) AB
(b) ac
(c)
OR
(d) log (1/2) (0.4)
1
(0.1)
9
9
(0.1)
1
= 1.
10
(e)
OR
(f) log (1/2) (0.45)
1
(0.05)
9
9
(0.05)
1
= 1.
10
(g) the SSR72 would be in the middle
A
a
B
c
A
c
B
a
A
clr
B
A
B
clr
21. The following three crosses involve mice from either true-breeding mutant
strains or true-breeding wild-type strains.
(a) X-linked recessive only
(b) X-linked recessive and autosomal recessive
(c) autosomal recessive only
22. E. coli can utilize the sugar melibiose after induction of the enzyme melibiase.
(a) yes, at 95%
(b) it gives a dominant phenotype
(c) It works in cis
(d) melibiose --] repressor
Mut
(e) the mutant repressor can’t bind to the operator any more
23. The sequence of the amber stop codon is
5’ UAG
3’ .
(a) the gln-tRNA gene and the trp-tRNA gene
(b) gln: 5’-CAG-3’ this strand is used as a template during transcription
3’-GTC-5’
trp: 5’-TGG-3’ this strand is used as a template during transcription
3’-ACC-5’
(c) 5’-TAG-3’ this strand is used as a template during transcription
3’-ATC-5’
24. You are studying the yeast genes needed to metabolize organic phosphates.
(a) an unlinked suppressor mutation that has no phenotype on its own – for instance, a
tRNA suppressor allele
(b) this suppressor mutation is very close to the original mutation, and thus might be an
intragenic suppressor mutation (and even may be a back mutation to revert the gene to
its original sequence)
Mel
(f) log (0.5)
1
= 0.
1
(g) log (1/2) (0.5)
1
= 0
1
27. You discover a frame-shift mutation in an X-linked gene called SPG in a man
who is infertile because of poor sperm production.
(a) Yes it is possible, because the mutation can be passed on by females indefinitely.
(b) i) pronuclear injection
ii) wt human SPG
iii) fertilized egg
iv) a fertilized egg that is XY and carries a mutant form of SPG on the X chrom
v) randomly
vi) no
vii) none
viii) if the male mouse is fertile, then the human and mouse SPG genes are
interchangeable. If the male mouse is sterile, then the human and mouse genes are not
interchangeable.
28. You have isolated two different X-linked mutations in Drosophila that affect eye
color.
(a) orange
(b) same gene
(c) 1 cM
(d)
sh rng w
29. You have constructed an F’ plasmid that carries the LacZ gene.
(a) The F’ plasmid
LacZ
(b) the Hfr:
PhoA LacI P O LacZ LacZ LacY LacA ProB
(c) no; it won’t express LacY because the gene is disjointed from its promoter
(d) late
30. The PyrG gene is found to lie about 40 kb away from the group of Lac genes on
the E. coli chromosome.
Draw a diagram of this region of the chromosome that shows where the PyrG gene
maps relative to LacZ and LacI.
ANSWER:
PyrG LacZ LacI
31. Only a small fraction of human fetuses with trisomy 18 survive to birth, and most
of those surviving to birth die in infancy.
(a) before
(b) mother
(c) meiosis I
(f) 23
(g) 44
(h) 24
32. In some families, breast cancer displays autosomal dominant inheritance.
(a) log (1/2) (0.05)
6
(0.45)
1
1
(0.45)
6
= 0.
7
(b) log (0.05)
1 (0.45)
6 = 0.
7
(c) the cell that develops into a tumor needs to lose the 2
nd copy of the gene by loss of
heterozygosity
(d) the phenotype caused by a homozygous loss of BRCA is lethality. Perhaps BRCA
is necessary for normal fetal development to occur.
33. You are genetically mapping the locus that determines a rare skin disease that
shows autosomal dominant inheritance.
(a) the father
(b) A
(c)
(d) log (0.45)
5
= 1.
5
(e) three families
SD
A
C
Tn-Kan
r
MalT
C
MalT
34. Consider an autosomal gene at which a rare allele (call it allele a) results in
homozygotes (aa) having only 20% of the number of offspring as average individuals in the
population.
(a) S = 0.
(b) h = 0.
(c) f(a) = 0.
(d) 2pq = 0.
(e) new q = 0.
35. You have isolated a Tn5 insertion in an otherwise wild-type E. coli strain that is
linked to the gene encoding the MalT activator protein.
(a) 80%
(b)
(c) an ochre nonsense mutation
(d) uninducible
36. You are called by your family physician to provide an expert genetic opinion on
an unusual patient: an XXX boy.
iii) the four final products of the meiosis
(d) the father must have passed on an X chromosome which mistakenly carried the Sry
gene that causes maleness
(e) a translocation occurred during the development of that sperm such that SSR1 went
to the Y chromosome in exchange for the Sry gene a
1A
2A
3B
4B
1C
2A
3B
4C
1A
2B
3A
4C
1C
2B
3A
4B
