Deck 12: Gene Mutation, DNA Repair, and Homologous Recombination

Question 1

You have conducted an Ames test on a given compound.Which of the following would be classified as a positive result on the Ames test?

A)His⁻ strain grows on an his⁻ plate.
B)His⁻ strain grows on an his⁺ plate.
C)His⁺ strain grows on an his⁻ plate.
D)His⁺ strain grows on an his⁺ plate.
E)His⁺ strain grows on either an his⁻ or an his⁺ plate.

Answer 1

A

Question 2

The adaptation mutation hypothesis predicts that

A)mutations occur at random in organisms.
B)separate bacterial cultures may contain different frequencies of a particular gene mutation.
C)environmental change cannot trigger mutations in a specific gene.
D)different bacterial cultures exposed to the same stress will have similar frequencies of a particular mutation.
E)bacterial cultures exposed to multiple types of environmental stress will consistently resist mutation.

Answer 2

D

Question 3

The compound 5-bromodeoxyuridine (BrdU)is a derivative of uracil,and if BrdU becomes incorporated during DNA replication,it pairs with adenine.This compound is best classified as which type of mutagen?

A)base analog
B)deaminating agent
C)oxidative agent
D)alkylating agent
E)intercalating agent

Answer 3

A

Question 4

If one Holliday junction region is resolved by an NS cut and the other by an EW cut,the resulting chromosomes

A)are nonrecombinant and carry the combinations A₁ and B₂ or A₂ and B₁.
B)are nonrecombinant and carry the combinations A₁ and B₁ or A₂ and B₂.
C)are A₁ and A₂ or B₁ and B₂.
D)are recombinant and carry the combinations A₁ and B₂ or A₂ and B₁.
E)are recombinant and carry the combinations A₁ and B₁ or A₂ and B₂.

Question 5

Given the DNA sequence 5′-TAC AAA ATA CAG CGG-3′,which of these sequences represents a missense mutation?

A)5′-TAG AAA ATA CAG CGG-3′
B)5′-TAC AAA TAC AGC GGG-3′
C)5′-TAC AAG ATA CAG CGG-3′
D)5′-TAC AAA ATA CAC CGG-3′
E)5′-TAC AAA ATA CAG AGG-3′

Question 6

You would like to induce a transversion mutation into a sequence of DNA.Which type of chemical mutagen would give you the best chance of inducing the correct mutation without causing transition mutations as well?

A)base analog
B)deaminating agent
C)oxidative agent
D)alkylating agent
E)intercalating agent

Question 7

Gene conversion can be observed in fungi by identifying aberrant ratios in the ascus.Which of the following represent possible aberrant ratios caused when there is no mismatch repair of base-pair mistakes in the heteroduplex region?

A)4:4
B)3:1:1:3
C)5:3
D)6:2
E)3:3:2

Question 8

Homologous recombination is initiated by

A)Rad51 generating double-stranded DNA breaks.
B)RecA,RecB,and RecC generating single-stranded DNA breaks.
C)Spo11 generating double-stranded DNA breaks.
D)p53 generating single-stranded DNA breaks.
E)ATM signaling double-stranded DNA breaks.

Question 9

Given the DNA sequence 5′-TAC AAA ATA CAG CGG-3′,which of these sequences represents a frameshift mutation?

A)5′-TAG AAA ATA CAG CGG-3′
B)5′-TAC AAA TAC AGC GGG-3′
C)5′-TAC AAG ATA CAG CGG-3′
D)5′-TAC AAA ATA CAC CGG-3′
E)5′-TAC AAA ATA CAG AGG-3′

Question 10

An intercalating agent such as aflatoxin is more likely to cause which type of mutation?

A)transition
B)transversion
C)frameshift
D)depurination
E)deamination

Question 11

Studies of gene mutation frequencies have shown that

A)mutations are rare,and genomes are generally stable.
B)mutation frequencies differ among organisms and also between genes,suggesting certain genes are more susceptible to mutation.
C)mutation frequencies are consistent between organisms,and each region of DNA is equally susceptible to random mutations.
D)Both A and B are correct.
E)Both A and C are correct.

Question 12

What phenotype would you expect to see in a strain of E.coli with a mutation in the phr gene?

A)decrease in UV-induced mutations
B)increase in UV-induced mutations
C)decrease in reversion of base-pair substitution mutations
D)increase in the methylation of nucleotide bases
E)decrease in the methylation of nucleotide bases

Question 13

Mutations can also occur within the regulatory regions of genes.Fragile X is an example of a disorder caused by one such mutation by increasing the length of the long arm of the X chromosome and ultimately decreasing mRNA stability.Which type of regulatory mutation causes Fragile X?

A)promoter
B)polyadenylation
C)splice site
D)triplet-repeat expansion
E)frameshift

Question 14

What type of mutation is seen here? Wild type: 5′-TAC AAA ATA CAG CGG-3′
Mutation: 5′-TAC AAG ATA CAG CGG-3′

A)transition
B)transversion
C)insertion
D)deletion
E)nonsense

Question 15

Given the DNA sequence 5′-TAC AAA ATA CAG CGG-3′,which of these sequences represents a nonsense mutation?

A)5′-TAG AAA ATA CAG CGG-3′
B)5′-TAC AAA TAC AGC GGG-3′
C)5′-TAC AAG ATA CAG CGG-3′
D)5′-TAC AAA ATA CAC CGG-3′
E)5′-TAC AAA ATA CAG AGG-3′

Question 16

Which types of mutation are possible thanks to the redundant nature of the genetic code?

A)silent
B)missense
C)nonsense
D)frameshift
E)splice site

Question 17

A strain of E.coli is unable to use the UV repair pathway because of an apparent absence of DNA helicase activity.Which UV repair gene is likely mutated in this strain?

A)uvr-A
B)uvr-B
C)uvr-C
D)uvr-D
E)pol I

Question 18

Which of these statements best describes gene expression in a damaged cell?

A)In a damaged cell,p53 is low and BAX transcription is inactive,so Bcl-2 represses apoptosis.
B)In a damaged cell,p53 is high and BAX transcription is active,so Bcl-2 is repressed and apoptosis is induced.
C)In a damaged cell,p53 is low and BAX transcription is active,so Bcl-2 represses apoptosis.
D)In a damaged cell,p53 is low and BAX transcription is active,so Bcl-2 is repressed and apoptosis is induced.
E)In a damaged cell,p53 is high and BAX transcription is inactive,so Bcl-2 is activated and apoptosis is induced.

Question 19

Which pathway is affected by an inherited mutation in the ATM gene?

A)nucleotide excision repair pathway
B)photoreactivation
C)p53 repair pathway
D)reactivation repair pathway
E)UV repair pathway

Question 20

Which type of mutation converts a nucleotide to an alternative structure with the same composition but slightly different placement of hydrogen bonds with a rare,less stable form that causes base-pair mismatch?

A)depurination
B)deamination
C)tautomeric shift
D)transition
E)transversion

Question 21

You use several model organisms in your lab's research.Which of your model organisms would you expect to exhibit a higher mutation frequency: E.coli,D.melanogaster,or M.musculus?

Question 22

Which enzyme is the product of the phr gene in E.coli?

Question 23

DNA glycosylase inhibitors are used to study which DNA repair mechanism?

Question 24

What are the two basic types of base-pair substitutions?

Question 25

Which type of double-stranded break repair would you expect to be used by a cell in the G₂ phase of the cell cycle?

Question 26

Which type of mutagen has a structure similar to one of the DNA nucleotides and therefore can work its way into DNA,where it pairs with a nucleotide?

Question 27

Which mechanism can be used to repair UV damage in Drosophila but not in humans?

Question 28

What two types of spontaneous damage to individual nucleotides are associated with subsequent mutation?

Question 29

Which repair mechanism is an error-prone system that uses bypass polymerases to replicate short segments of daughter strands whose normal replication is blocked by lesions in template strand DNA?

Question 30

If you have screened 100,000 pollen grains and identified 5 mutants,what is the mutation frequency?

Question 31

Which type of double-stranded break repair would you expect to be used by a cell in the G₁ phase of the cell cycle?

Question 32

You have developed a new drug and have been asked to test the drug's mutagenicity before putting it on the market.Which test could you use to determine your compound's mutagenic potential?

Question 33

The alkylating agent nitrosoguanidine adds methyl groups to nucleotide bases and is repaired by which enzyme that removes the added methyl group and restores nucleotides to their normal form?

Question 34

What term describes a gene or region of a genome where mutations occur much more often than average?

Question 35

What type of mutation commonly affects CpG islands,altering promoter regions of mammalian genes?

Question 36

Localized mutations that occur at a specific or identifiable location on a gene are better known as what?

Question 37

What type of mutagen would you use if you wanted to study the effect of pyrimidine dimers in causing cancer?

Question 38

What process,which is responsible for many trinucleotide repeat disorders,alters the number of DNA repeats?

Question 39

Which process is carried out by specialized bypass DNA that can replicate across the gaps induced during replication by UV damage?

Question 40

What is the human cancer syndrome associated with inherited p53 mutations?

Question 41

Agents generating mutation-inducing DNA damage are collectively referred to as ________.

Question 42

A second-site mutation that compensates for the mutation in one gene by mutating a second gene and restoring the wild-type phenotype is also known as a ________ mutation.

Question 43

You accidentally exposed your cell culture dish to radiation,but you are not sure of the precise wavelength of the exposure.How can you use the induced DNA damage to tell whether the radiation was UV or higher energy? What is the difference between the DNA damage caused by UV radiation compared to higher-energy radiation? Which type of damage is the most likely to be the most lethal to your cells?

Question 44

DNA damage signaling processes are essential for regulating the ________ transition within the cell cycle.

Question 45

You are interested in studying the function of a gene,so you decide to create point mutations to help you identify important residues in your protein.
Which of the adenines in the following sequence could you mutate to create a silent transversion mutation?
5′-ATG GGA TGG CAC CTG-3′

Question 46

Double-strand breaks cause genomic instability and are thus potentially lethal to cells.They also greatly increase the risk of cancer and the chance of chromosome structural mutations.Compare and contrast the two mechanisms of double-strand break repair.Why would one mechanism be used over another?

Question 47

Which of the adenines in the following sequence could you mutate to create a missense transition mutation?
5′-ATG GGA TGG CAC CTG-3′

Question 48

________ are structures that have the same composition and general arrangement but a slight difference in bonding and placement of a hydrogen.

Question 49

Explain what is meant by deamination.How does this mutation affect a cytosine (C)versus a methylcytosine (5meC)? What effect does deamination have on CpG islands,and how does that affect the mutation frequencies in these regions?

Question 50

Which bases would you mutate to create a nonsense transition mutation?
5′-ATG GGA TGG CAC CTG-3′

Question 51

The Ames test is designed to identify the rate of ________ that restore the ability of bacteria to synthesize their own histidine,thus eliminating the need for histidine supplementation of the growth medium.

Question 52

A bacterial culture is exposed to UV radiation and is preparing to repair the DNA damage.Describe two mechanisms of repair used by E.coli to repair UV-induced DNA damage.Would you expect the bacteria to be able to repair more or less of the damage if they were to be placed in a dark environment after UV damage?