Deck 16: Mutation, Repair, and Recombination

Question 1

The fluctuation test of Luria and Delbruck showed that:

A)a selecting agent can affect mutation rate in E.coli.
B)mutations can arise spontaneously before exposure to the selecting agent.
C)mutations in E.coli occur at a relatively high frequency.
D)the mutation rate in E.coli fluctuates greatly from one generation to the next.
E)the T1 phage can act as a mutagen as well as a selecting agent in E.coli.

Answer 1

B

Question 2

In E.coli,a region of a gene with repeats of the sequence CTGG will be prone to:

A)deletions.
B)frameshift mutations.
C)missense mutations.
D)reversion.
E)triplet expansion.

Answer 2

B

Question 3

In E.coli,a region flanked by two repeats of a sequence such as GTGGTGAA is prone to:

A)deletions.
B)duplications.
C)frameshift mutations.
D)missense mutations.
E)reversion.

Answer 3

A

Question 4

A point mutation in a gene's promoter will most likely cause the production of:

A)a shortened mRNA and a truncated protein.
B)a shortened mRNA and a wild-type protein.
C)reduced amounts of mRNA and protein.
D)reduced amounts of mRNA and wild-type amounts of protein.
E)wild-type amounts of mRNA and reduced amounts of protein.

Question 5

A small (one base pair)insertion in the middle of the coding region of a gene will cause a:

A)synonymous mutation.
B)silent mutation.
C)nonsense mutation.
D)missense mutation.
E)frameshift mutation.

Question 6

A mutation that changes the codon UAA to the codon UAG in a mammalian cell line is called a(n):

A)synonymous mutation.
B)suppressor mutation.
C)nonsense mutation.
D)missense mutation.
E)antisense mutation.

Question 7

A mutation changes a codon from AAA (encoding lysine)to AGA (encoding arginine)in yeast,but no mutant phenotype is detected when the mutant strain is plated and grown on minimal or complete medium.This type of mutation is called:

A)synonymous.
B)suppressor.
C)nonsense.
D)missense.
E)frameshift.

Question 8

After mutagen treatment,a molecule of 2-aminopurine (an adenine analogue)incorporates into DNA.During replication,the 2-AP protonates.The mutational event caused by this will be:

A)AT to CG.
B)GC to AT.
C)AT to TA.
D)AT to GC.
E)GC to CG.

Question 9

In a haploid fungus,a small in-frame deletion arises in the coding region of a gene necessary for the production of the amino acid leucine.The deletion removes the three base pairs corresponding to a UAC codon (encoding cysteine).This small deletion will most likely cause:

A)the production of a truncated (shortened)protein.
B)the production of a truncated (shortened)mRNA.
C)the production of a shorter mRNA and of a shorter protein.
D)no detectable phenotype.
E)inability to grow on medium that lacks cysteine.

Question 10

A mutation does not affect the length of a gene but results in an abnormally short protein.The mutation is most likely of a type called:

A)silent.
B)nonsense.
C)missense.
D)frameshift.
E)deletion.

Question 11

The rare enol form of thymine pairs with guanine.If a thymine enolization occurs during replication,what would be the mutational event?

A)AT to TA
B)CG to AT
C)CG to GC
D)GC to TA
E)TA to CG

Question 12

During mutagenic treatment with nitrous acid,an adenine deaminates to form hypoxanthine,which bonds like guanine.The mutational event would be:

A)AT to CG.
B)AT to GC.
C)AT to TA.
D)GC to AT.
E)GC to TA.

Question 13

The spontaneous reversion rate for a chemically induced mutation is 1 × 10^-8.For EMS ,the rate is 0.9 × 10^-8,and for acridine,it is 2 × 10^-5.What change was involved in the original mutation?

A)an AT to CG transversion
B)an AT to GC transition
C)a frameshift mutation
D)a GC to AT transition
E)a GC to TA transversion

Question 14

In a haploid fungus,a transversion arises in the coding region of a gene necessary for the production of the amino acid leucine.The transversion substitutes the last base in the codon UAC (encoding cysteine),resulting in the stop codon UAG.This substitution will most likely cause:

A)the production of a truncated (shortened)protein.
B)the production of a truncated (shortened)mRNA.
C)the production of a shortened mRNA and of a shortened protein.
D)no detectable phenotype.
E)inability to grow on medium that lacks cysteine.

Question 15

Fragile X syndrome is caused by:

A)exposure to high doses of 5-bromouracil.
B)exposure to high doses of free radicals.
C)an inherited microdeletion.
D)spontaneous depurination.
E)trinucleotide expansion.

Question 16

A mutant plant with white flowers exists that lacks red anthocyanin pigment,normally made by enzyme P.Indeed the petal tissue lacks all detectable activity for enzyme P.Despite the lack of enzyme activity,a study of homozygous mutant cells using antibodies against the wild-type enzyme demonstrated that the cells homozygous for the mutation still had the enzyme (i.e.,the antibody showed the presence of the enzyme).Which statement could explain these results?

A)The mutant had another gene the researcher was not aware of which produced an enzyme that could function like the mutated enzyme.
B)The mutant cells likely had large scale chromosomal mutations that resulted in the expression of some gene similar to the gene for enzyme P.
C)The mutant allele must have had a nonsense mutation that resulted in complete formation of a non-functioning enzyme.
D)The mutant allele must only have missense mutations that simply knocked out enzyme function yet the enzyme would still bind to the antibody.
E)None of the answers are correct.

Question 17

A transversion somewhere within gene "B" in a laboratory plant results in the production of a mutant mRNA that is much longer than the wild type.This transversion is most likely located:

A)downstream of the STOP codon,in the last exon of gene "B."
B)in an intron of gene "B" away from the splice sites.
C)in the open reading frame of gene "B."
D)within a splice site of gene "B."
E)within the promoter of gene "B."

Question 18

A plant is homozygous for a point mutation in gene B.This plant produces wild-type B protein in wild-type amounts,but a more detailed analysis reveals that the B mRNA produced by this plant is two nucleotides shorter than wild type.The mutation is most likely a two base-pair deletion:

A)downstream of the STOP codon,in the last exon of gene B.
B)in an intron of gene B away from the splice sites.
C)in the open reading frame of gene B.
D)that removed a splice site of gene B.
E)within the promoter of gene B.

Question 19

Imagine that exposure to the antibiotic streptomycin promotes mutations causing streptomycin resistance in E.coli.If you repeated Luria and Delbruck's test using streptomycin instead of the T1 phage,what results would you expect?

A)None of the 20 individual cultures would show any streptomycin-resistant colonies.
B)The 20 individual cultures would show a high variation in the number of streptomycin-resistant colonies.
C)The 20 individual cultures would show a high variation in the size of streptomycin-resistant colonies.
D)The 20 individual cultures would show comparable numbers of streptomycin-resistant colonies.
E)The 20 individual cultures would show streptomycin-resistant colonies of unusually large size.

Question 20

In a classical genetic experiment,Newcombe spread E.coli cells on complete medium.After several generations of growth,he replica-plated the colonies onto two plates with complete medium plus a selective agent.Colonies on the first replica were left untouched,while on the second replica,they were respread,allowing bacteria from each colony to be "moved" to a new location on the plate.Significantly more mutants after spreading (resistant to the selective agent)were observed than if they had not been respread.The experiment was used to:

A)demonstrate how to screen for environmental mutagens.
B)demonstrate that in some cases mutations are caused by the selective agent itself.
C)provide evidence that mutations occur in the absence of the selective agent.
D)provide evidence that mutation occurs in prokaryotes as well as in eukaryotes.
E)show a direct correlation between the amount of the selective agent used and the number of resistant mutants.

Question 21

The Spo11 enzyme in eukaryotic cells makes:

A)single-stranded cuts in the DNA to initiate replication.
B)double-stranded cuts in the DNA to initiate replication.
C)single-stranded cuts in the DNA to initiate recombination.
D)double-stranded cuts in the DNA to initiate recombination.
E)causes cancer.

Question 22

A mouse is homozygous for a transversion that eliminated the splice site between the first exon and the first intron of gene "G." The resulting mutant mRNA is longer than the wild type,but the protein that it encodes is much shorter than its wild-type counterpart.Provide a logical and plausible explanation for these observations.

Question 23

Proto-oncogenes are genes that:

A)always mutate into cancer-promoting oncogenes.
B)encode very important proteins involved in processes such as the control of cell cycle.
C)encode very important proteins that promote apoptosis.
D)in their recessive form can act to promote cell cycle progression.
E)normally promote oncogenesis.

Question 24

Shown below is a list of statements (a-k)and types of mutations (1-6).On the blank line following each mutation,write the letter(s)of all statements that apply to that type of mutation.Note that each statement may be used more than once and each type of mutation may have more than one correct statement.
a)a mutation that changes UUA to UUG
b)a mutation that gives methionine instead of leucine
c)created by the addition of a nucleotide to a coding region
d)a stop codon is read as an amino acid
e)a chemically similar amino acid is replaced by the mutation
f)a mutation that changes CCU to ACU
g)da nucleotide in a coding region gives this type of mutation
h)mutation does not alter the peptide
i)a mutation changing UAU to UAG
j)premature termination codon is responsible for this mutation
k)a chemically different amino acid is replaced by the mutation
1)missense mutation __________
2)silent mutation __________
3)frameshift mutation __________
4)nonsense mutation __________
5)synonymous mutation __________
6)nonsense suppressor mutation __________

Question 25

People who develop the hereditary form of retinoblastoma inherit:

A)a pair of dominant alleles causing retinoblastoma.
B)a pair of normal (non-retinoblastoma)alleles.
C)a pair of recessive alleles causing retinoblastoma.
D)a single dominant allele causing retinoblastoma.
E)a single recessive allele causing retinoblastoma.

Question 26

Which of the following diseases is/are LEAST likely to be caused by excessive exposure to UV light?

A)Cockayne syndrome
B)Huntington disease
C)lung cancer
D)skin cancer
E)xeroderma pigmentosum

Question 27

The Ames test is used for determining whether a particular chemical acts as a mutagen.It does this by selecting for:

A)new His^- mutations in Escherichia coli.
B)revertants of His^- mutations in Escherichia coli.
C)new His^- mutations in Salmonella typhimurium.
D)revertants of His^- mutations in Salmonella typhimurium.
E)both revertants and new His^- mutations in Escherichia coli.

Question 28

E.coli cells that have null mutations in the gene encoding adenine methylase will have:

A)a higher spontaneous mutation rate than wild-type E.coli.
B)the same spontaneous mutation rate as wild-type E.coli.
C)a lower spontaneous mutation rate than wild-type E.coli.
D)more double-strand breaks in their DNA than wild-type E.coli.
E)fewer double-strand breaks in their DNA than wild-type E.coli.

Question 29

A Neurospora nonsense mutation known to be UAG is treated with two compounds,hydroxylamine and 5-bromouracil.Hydroxylamine (HA)causes G·C → A·T transitions,while 5-bromouracil causes T·A → C·G transitions.Which of these agents do you expect to induce revertants?

A)Both agents are expected to induce revertants.
B)Both agents are expected to induce revertants,but hydroxylamine will be more effective.
C)5-bromouracil only is expected to induce revertants.
D)Hydroxylamine only is expected to induce revertants.
E)Neither hydroxylamine nor 5-bromouracil agents are expected to induce revertants.

Question 30

If an incorrect base is incorporated during DNA synthesis and is not corrected by DNA polymerase,it can be corrected by postreplication repair.Postreplication repair does NOT involve which of the following?

A)detection of the mismatch
B)photoreactivation repair
C)a process similar to excision repair
D)recognition of the methylation status of the DNA strands
E)recombinational repair

Question 31

A mutation that occurred in a plant petal would be best termed:

A)dominant.
B)germinal.
C)recessive.
D)somatic.
E)suppressor.

Question 32

A partial peptide sequence for the wild type and three mutant alleles of a gene,PET1,are shown below.Each mutant was caused by a single point mutation.

$\text { Wild type:\quad met \quad ile \quad arg \quad met \quad asp \quad lys \quad trp... }$
$\text { Mutant 1:\quad met \quad ile \quad gln \quad asn \quad gly ... }$
$\text {Mutant 2:\quad met \quad ile \quad arg \quad met \quad gly \quad lys \quad trp...}$
$\text {Mutant 3: \quad met \quad ile \quad ser \quad met \quad asp \quad lys \quad trp...}$

a)Using the amino acid sequence of the wild type and the three mutants,deduce the exact DNA sequence of the coding strand of the wild-type allele.
b)What type of mutation (transition vs.transversion vs.indel;missense vs.nonsense vs.frameshift)has occurred in each mutant?
c)What consequence will each of the above-mentioned DNA mutations have on protein function?

Question 33

Below are a list of mutagen mechanism descriptions (a-e)and a list of mutagen names (1-5).On the blank line following each mutagen,write the letter(s)of all descriptions that apply to that type of mutagen.Note that each statement may be used more than once and each type of mutation may have more than one correct statement.
a)Single-nucleotide insertions or deletions resulting in frameshift mutations if the mutation occurred in the coding region.The mutagen is a flat planar molecule that slips between stacked nitrogen bases.
b)Causes transitions (usually GC to AT)by adding an alkyl group to a base (usuallyG),thus altering its pairing properties.
c)Causes AT to GC transitions by acting as a base analogue for adenine.It is unstable and readily undergoes tautomeric shifts.Its imino form pairs with C rather than G.
d)Causes GC to TA transversions.Creates an apurinic site by breaking the base-sugar bonds.In order to correct the mutation,the SOS repair system preferentially adds an A opposite to G.
e)Makes pyrimidine dimers by making a bond between adjacent pyrimidines,thus interfering with the normal base pairing between the complementary DNA strands.
1)2-aminopurine __________
2)UV light __________
3)acridine orange __________
4)aflatoxin __________
5)ethylmethanesulfonate (EMS)__________

Question 34

E.coli cells that have null mutations in the gene encoding mutH will be defective in:

A)base excision repair.
B)mismatch repair.
C)recombinational repair.
D)SOS repair.
E)thymine dimer splitting.

Question 35

Which of the following diseases is/are MOST likely to be caused by excessive exposure to UV light?

A)Cockayne syndrome
B)Huntington disease
C)lung cancer
D)skin cancer
E)xeroderma pigmentosum

Question 36

Shown below is a list of types of repair systems or repair molecules (a-g)and types of DNA damage or mutations (1-5).On the blank line following each type of damage,write the letter(s)of all repair systems that can repair (or play a role in the repair of)that particular type of damage.
a)photolyase
b)base-excision repair
c)SOS repair
d)alkyltransferases
e)mismatch repair
f)homologous recombination
g)nucleotide-excision repair
1)alkylation of G residues __________
2)depurination __________
3)pyrimidine dimers __________
4)deamination __________
5)double-stranded breaks __________

Question 37

In E.coli,mutations arising during repair are mostly caused by:

A)base excision repair.
B)mismatch repair.
C)recombinational repair.
D)SOS repair.
E)thymine dimer splitting.

Question 38

A missense mutation in Neurospora will revert by treatment with nitrous acid,but not by hydroxylamine.Hydroxylamine (HA)causes only G·C → A·T transitions,while nitrous acid causes both G·C → A·T and A·T → G·C transitions.The original mutation (not the reversion)must have been:

A)AT to CG.
B)AT to GC.
C)AT to TA.
D)GC to AT.
E)GC to TA.

Question 39

Which of the following mutations is/are MOST likely to result in cell overgrowth and (eventually)may lead to cancer?

A)a gain-of-function mutation in one allele of a proto-oncogene
B)a gain-of-function mutation in one allele of a tumor suppressor gene
C)a loss-of-function mutation in one allele of a proto-oncogene
D)a loss-of-function mutation in one allele of a tumor suppressor gene
E)a null mutation in one allele of a proto-oncogene

Question 40

Mice that are homozygous for a complete deletion of the wild-type gene "T" develop multiple tumors in a variety of tissues very early in life.Gene "T" is most likely:

A)an activated oncogene.
B)a dominant tumor suppressor gene.
C)an oncogene.
D)a proto-oncogene.
E)a tumor suppressor gene.

Question 41

a)A met⁺ strain of Neurospora was treated with a mutagen to create met^- mutants.The mutants were reverted to met⁺ with HA (hydroxylamine),which causes GC to AT transitions.What was the original mutation on the molecular level?
b)Two of the revertants showed odd results when crossed with a wild-type met⁺ strain.
$$\begin{array} { l l } \text { Cross } & \text { Progeny } \\\text { met } ^ { + } \text {revertant A } \times m et ^ { + } \text {wild type } & 8 8 \% \text { met }^+ \\& 12 \% \text { met }^-\end{array}$$ $\begin{array}{ll}\text { met }^{+} \text {revertant B } \times \text { met }^{+} \text {wild type }& 93 \% \text { met }^{+}\\&7\% \text { met }^-\end{array}$
Explain how these results occurred and why the above numbers of offspring were obtained.

Question 42

Some indel mutations can be created spontaneously as a result of errors during DNA replication.
a)Use diagrams to show how 1)insertions and 2)deletions are spontaneously created as a result of the replication of tandem repeats.
b)Give the term used to describe this process.
c)Name two human diseases that arise as a consequence of expanded trinucleotide repeats in DNA.
d)Describe two ways in which expanded trinucleotide repeats can cause disease.

Question 43

Five different mutations were derived from base pair substitutions at a single codon.In this codon,the mutant alleles had arginine,leucine,glycine,serine,and cysteine.What was the wild-type codon?

Question 44

How do mutation and DNA damage differ?

Question 45

Consider the following mutations and,for each,explain whether you expect it to be
a)potentially promoting cancer
b)dominant or recessive
i)a mutation that destroys the active site of an enzyme necessary to promote cell cycle
ii)a very premature STOP codon in a gene encoding a protein involved in the excision-repair mechanism
iii)a point mutation that renders constitutively active one of the signaling proteins in the Ras pathway
iv)a null mutation in a gene encoding an apoptotic (apoptosis-promoting)protein

Question 46

Crossing over is a very precise process.Why is it important that the process of crossing over is so precise? What impact would there be if it were not precise? Draw a picture depicting an imprecise crossover and show the result of this imprecise event.

Question 47

Photoreactivation repair is effective only in the presence of visible light.What other repair mechanism is available to repair pyrimidine dimers if visible light was not available? Describe the steps of this mechanism.

Question 48

5-Bromouracil is an analog of thymine that normally pairs with adenine.Its rare tautomeric form pairs with adenine.Show the steps (i.e.,several replications)by which 5-bromouracil causes the GC base pair shown below to change to an AT base pair.Show the point at which the rare tautomeric form of 5-bromouracil occurs.Show both products of all divisions in which 5-bromouracil is involved.Do not show chemical structures.

Question 49

Three mutations were obtained in a bacterial gene.An antibody is available for the protein product of this gene.Both Northern analysis (RNA separated by electrophoresis,blotted,and probed with DNA)and Western analysis (proteins separated by electrophoresis,blotted,and probed with antibodies)were performed on the mutants.The results are summarized below.
For each mutation,what kind of mutation occurred and how do you know it?
a)Mutant 1 b)Mutant 2 c)Mutant 3