Chapter 18

Question 1

The type of mutation that reverses the effects of a frameshift mutation without changing the frameshift and occurs with the same gene as the frameshift is called a(n)

a. intergenic suppressor mutation
b. nonsense mutation
c. missense mutation
d. intragenic suppressor mutation
e. silent mutation

Answer 1

d. intragenic suppressor mutation

Question 2

How do germ-line mutations differ from somatic mutations?

a. Germ-line mutations involve small changes to DNA such as base-pair substitutions, while somatic mutations usually involve large deletions.
b. Germ-line mutations occur during DNA replication, while somatic mutations do not.
c. Germ-line mutations result in mutant gametes, while somatic mutations do not.
d. Germ-line mutations are reversible, while somatic mutations are not.
e. Germ-line mutations result in cancers, while somatic mutations do not.

Answer 2

c. Germ-line mutations result in mutant gametes, while somatic mutations do not.

Question 3

Which of the following base changes in DNA is an example of a transition?

a. A-to-C
b. G-to-C
c. C-to-A
d. A-to-G
e. A-to-T

Answer 3

d. A-to-G

Question 4

Which of the following correctly describes nonsense mutations?

a. They cause a nonfunctional amino acid to replace a functional amino acid.
b. They change the nucleotide sequence of a gene but do not change the sequence of the resulting protein.
c. They result in the insertion or deletion of a small number of nucleotides to the DNA.
d. They convert a codon for a particular amino acid within a gene into a stop codon.
e. They cannot revert or back mutate to wild-type.

Answer 4

d. They convert a codon for a particular amino acid within a gene into a stop codon.

Question 5

Assume that a base-pair substitution mutation converts a DNA triplet (AAT) to another DNA triplet (AAA). A second mutation now changes the AAA triplet to the GAA triplet. (UUA and CUU code for leucine and UUU codes for phenylalanine.) This second mutation is an example of a(n)

a. transversion.
b. intragenic suppressor.
c. loss-of-function mutation.
d. intergenic suppressor.
e. frameshift.

Answer 5

b. intragenic suppressor.

Question 6

A example of a genetic disorder in humans that results from a loss-of-function mutation is

a. cystic fibrosis.
b. achondroplasia.
c. Huntington disease.
d. myotonic dystrophy.
e. None of the above is correct.

Answer 6

a. cystic fibrosis.

Question 7

Which of the following statements about somatic mutations is FALSE?

a. Some may give rise to cancers in humans and other animals.
b. They may be inherited by daughter cells after cell division.
c. They may result in inactive gene products of the mutated genes.
d. They may result from both frameshift and base-pair substitution mutations.
e. They may be inherited in the offspring of mutated individuals.

Answer 7

e. They may be inherited in the offspring of mutated individuals.

Question 8

Fragile-X syndrome is an example of a disease caused by what type of mutation?

a. Nonsense mutation
b. Frameshift mutation
c. Expanding nucleotide repeat
d. Loss-of-function
e. Gain-of-function

Answer 8

c. Expanding nucleotide repeat

Question 9

Which of the following types of mutations does NOT lead to a change in the amino acid sequence of the gene product?

a. Missense
b. Nonsense
c. Neutral
d. Silent
e. Loss-of-function

Answer 9

d. Silent

Question 10

Insertion or removal of one or more nucleotide base pairs in DNA within a gene often results in a ____________ mutation.

a. transition
b. frameshift
c. reversion
d. transversion
e. suppressor

Answer 10

b. frameshift

Question 11

A _________ mutation changes a codon that specifies an amino acid into one that terminates translation.

a. missense
b. nonsense
c. silent
d. neutral
e. reverse

Answer 11

b. nonsense

Question 12

__________ mutations produce new activities and are usually dominant.

a. Induced
b. Spontaneous
c. Forward
d. Gain-of-function
e. Lethal

Answer 12

d. Gain-of-function

Question 13

Which of the following kinds of mutations is most likely to be null loss-of-function?

a. Transition
b. Transversion
c. Frameshift
d. Missense
e. Induced

Answer 13

c. Frameshift

Question 14

Which of the following statements about an animal bearing a somatic mutation is TRUE?

a. Some, but not all, of the animal’s offspring will also carry the mutation.
b. All of the animal’s offspring will carry the mutation.
c. Both the animal and its offspring will show the mutant trait.
d. The animal but not its offspring can be affected by the mutation.
e. The gametes produced by the animal will all carry the mutation.

Answer 14

d. The animal but not its offspring can be affected by the mutation.

Question 15

A mutation that changes a GC base pair to AT is a(n)

a. transition.
b. transversion.
c. induced mutation.
d. missense mutation.
e. synonymous mutation.

Answer 15

a. transition.

Question 16

Huntington disease can strike at an earlier age and bring about a more rapid degeneration and death in successive generations within a family. This phenomenon can be explained by which mechanism?

a. Presence of a transposable element in the gene
b. Chronic exposure to mutagens in the environment
c. Expansion of a trinucleotide repeat in the coding sequence of the gene
d. Presence of an extra chromosome in the germ line
e. Absence of a gene product that is involved in DNA repair

Answer 16

c. Expansion of a trinucleotide repeat in the coding sequence of the gene

Question 17

What is the consequence of a transversion mutation in duplex DNA?

a. A purine is replaced by a pyrimidine, and a pyrimidine is replaced by a purine.
b. A base pair is lost within the DNA of a gene, which causes a reading frame shift.
c. A purine is replaced by another purine, and a pyrimidine is replaced by another pyrimidine.
d. A base pair is added to the DNA within a gene, which causes a reading frame shift.
e. The sequence of the DNA remains the same since the change involves proteins.

Answer 17

a. A purine is replaced by a pyrimidine, and a pyrimidine is replaced by a purine.

Question 18

Achondroplasia is a form of dwarfism that is inherited in humans as an autosomal dominant. A survey in a small country showed that, within a two-year period, there were 12 children with normal parents born with this disorder out of a total of 420,000 births. What is the mutation rate in mutations/locus/generation?

a. 1.4 10-5
b. 2.8 10-6
c. 2.5 10-5
d. 2.8 10-5
e. 7.4 10-6

Answer 18

a. 1.4 10-5

Question 19

Suppose a research study shows that people who suffer from severe depression are homozygous for a mutation in the hypothetical DEP gene. Individuals without this form of depression have the following sequence at the beginning of the translated region of their DEP genes 5-ATG ACG TTT GAA ATT CAG TCT AGA-3 (Met Thr Phe Glu Ile Gln Ser Arg). Affected individuals have the following sequence 5-ATG ACG TTT GAA ATT TAG TCT AGA-3 (Met Thr Phe Glu Ile STOP). The mutation identified is most likely a

a. missense.
b. gain of function.
c. nonsense.
d. frameshift.
e. deletion.

Answer 19

c. nonsense.

Question 20

Helen has type I osteogenesis imperfecta (OI), a genetic skeletal disorder. Shown below is her DNA sequence for a portion of the coding region of the collagen type I gene, which contains the mutation responsible for her disorder. The corresponding wild-type sequence is shown also (only one DNA strand is shown in each case).

Helen 5-AAACTCCACTTCTTCCAGTAC-3
Normal 5-AAACTCACTTCTTCCAGTAC-3

What type of mutation does Helen carry?

a. Missense
b. Nonsense
c. Silent
d. Deletion
e. Frameshift

Answer 20

e. Frameshift

Question 21

Which of the following mutagens is most likely to cause a frameshift mutation?

a. Base analog
b. Alkylating agent
c. Intercalating agent
d. Ionizing radiation
UV light

Answer 21

c. Intercalating agent

Question 22

Assume that during DNA replication in a bacterium a mistake is made and a G is inserted into the newly synthesized DNA strand opposite a T in the template DNA strand. If this mistake is not repaired before the next round of DNA replication, what mutation will eventually result?

a. A-to-G base substitution
b. A-to-C base substitution
c. A-to-T base substitution
d. G-to-A base substitution
e. C-to-A base substitution

Answer 22

a. A-to-G base substitution

Question 23

What do alkylating agents do?

a. They cause pyrimidine dimers.
b. They add methyl or ethyl groups to bases.
c. They oxidize guanine.
d. They deaminate cytosine.
e. They can do all of the above.

Answer 23

b. They add methyl or ethyl groups to bases.

Question 24

Ultraviolet light causes what type of DNA lesion?

a. Large deletions
b. Deaminated cytosines
c. Pyrimidine dimers
d. Mismatch bases
e. Depurinations

Answer 24

c. Pyrimidine dimers

Question 25

Assume that you have discovered a new chemical mutagen that modifies guanine so that is mispairs with adenine when adenine is in the template DNA strand during DNA replication. However, this mispairing is limited to when the modified guanine is being added to the newly replicating DNA strand. When the modified guanine is in the template DNA strand it always pairs normally with cytosine being added to the growing newly synthesized strand. What type of mutation would you predict would be caused by the new chemical mutagen? a. A-to-G base substitutions b. A-to-C base substitutions c. A-to-T base substitutions d. A-to-G and A-to-C base substitutions e. G-to-T base substitutions

Answer 25

b. A-to-C base substitutions

Question 26

In the Ames test, what types of mutations are used to test for chemical mutagens? a. his- to his+ mutations b. pro- to pro+ mutations c. pro+ to pro- mutations d. his+ to his- mutations e. trp+ to trp- mutations

Answer 26

a. his- to his+ mutations

Question 27

Which of the following transposable elements have indirect repeats at each end? a. Ac in maize b. Ty in yeast c. copia in Drosophila d. Alu in humans e. All of the above have indirect repeats.

Answer 27

a. Ac in maize

Question 28

Practically all transposable elements that have studied are associated with which of the following? a. Indirect repeats at each end b. A gene for transposase c. A gene for reverse transcriptase d. A gene for RNA polymerase e. Flanking direct repeats

Answer 28

e. Flanking direct repeats

Question 29

Bacterial insertion sequences encode which of the following gene products? a. Reverse transcriptase b. DNA polymerase c. Transposase d. Repressor e. Insertase

Answer 29

c. Transposase

Question 30

Transposable elements are found a. mainly in higher plants. b. mainly in animals, particularly in mammals. c. mainly in eukaryotes. d. mainly in prokaryotes. e. in practically all organisms.

Answer 30

e. in practically all organisms.

Question 31

Hybrid dysgenesis in Drosphila occurs a. when a male and a female, each carrying a copia element, mate and produce offspring that have numerous mutations. b. in the offspring of a cross between a male that carries a copia element and a female that carries a P element. c. in the offspring of a cross between a male that carries a Ty element and a female that carries an Ac element. d. in the offspring of a cross between a male that carries a P element and a female that does not carry a P element. e. in the offspring of a cross between a male that carries a Alu element and a female that carries a Ty element.

Answer 31

d. in the offspring of a cross between a male that carries a P element and a female that does not carry a P element.

Question 32

Which of the following is characteristic of retrotransposons? a. They use transposase to transpose to new sites. b. They have inverted repeats at each of their ends. c. They transpose through an RNA intermediate d. They make transposase. e. They are found only in prokaryotes.

Answer 32

c. They transpose through an RNA intermediate

Question 33

Which of the following is the most common transposable element in humans? a. copia b. Alu c. Ac d. Ty e. P

Answer 33

b. Alu

Question 34

Upon transposing to a new site, transposable elements a. add methyl groups to bases of the surrounding DNA. b. delete about 100 base pairs of DNA on each side of them. c. duplicate their transposase gene. d. express a gene that confers sensitivity to some common antibiotics. e. create a duplication of a target sequence on each side of them.

Answer 34

e. create a duplication of a target sequence on each side of them.

Question 35

Which of the following describes the possible parasitic nature of transposable elements? a. Transposable elements can increase in number within genomes without providing an advantage to the host. b. Transposable elements are collected within their genomes by host organisms so that the host will benefit, but not the transposable elements. c. Transposable elements will provide an evolutionary advantage to host organisms by transposing as often as possible. d. Transposable elements will enhance their expression of transposase so that the hosts can evolve more quickly. e. Transposable elements will add methyl groups to their own DNA to reduce their own rate of transposition.

Answer 35

a. Transposable elements can increase in number within genomes without providing an advantage to the host.

Question 36

Composite transposons in bacteria are characterized by which of the following? a. They are composites of Ac and Ds elements. b. Each has the ability to transpose either by replicative transposition or nonreplicative transposition. c. They contain all deleted transposase genes. d. They contain more than one gene. e. None of the above is correct.

Answer 36

d. They contain more than one gene.

Question 37

Which of the following characterizes the mode of transposition of retrotransposons? a. It involves a RNA intermediate. b. It involves the initial synthesis of transposase. c. It involves the production of a protein repressor. d. It only occurs in nondividing host genomes. e. It requires inverted repeats at each end of the retrotransposon.

Answer 37

a. It involves a RNA intermediate.

Question 38

It is estimated that transposable elements compose approximately what percent of the human genome? a. <1% b. 1% c. 10% d. 50% e. 99%

Answer 38

d. 50%

Question 39

Transposition can involve exchange of DNA sequences and recombination, which often leads to DNA a. acetylation. b. rearrangements. c. condensation. d. repair. replication

Answer 39

b. rearrangements.

Question 40

Which of the following transposable elements are flanked by direct repeats of a short portion of the host genome? a. Tn10 b. L1 c. Activator (Ac) d. Alu e. All of the above

Answer 40

e. All of the above

Question 41

Which of the following best describes the Activator (Ac) and Dissociation (Ds) transposable elements in maize (corn)? a. Ac elements cannot transpose unless a Ds element is present. b. Ac contains a functional transposase gene; Ds lacks a functional transposase gene. c. Ds contains a functional transposase gene; Ac lacks a functional transposase gene. d. Both Ac and Ds have functional transposase genes. e. Neither Ac nor Ds contains functional transposase genes.

Answer 41

b. Ac contains a functional transposase gene; Ds lacks a functional transposase gene.

Question 42

1. Which of the following is required for an IS element in E. coli to be able to transpose? a. A gene for reverse transcriptase and long terminal repeats b. A gene for reverse transcriptase and inverted repeats c. A gene for transposase and inverted repeats d. A gene for transposase and long terminal repeats e. A gene for DNA polymerase and long terminal repeats

Answer 42

c. A gene for transposase and inverted repeats

Question 43

Consider two theoretical transposable elements in yeast, A and B. Each contains an intron and each transposed to a new location in the yeast genome. Suppose you then examine the transposons for the presence of the intron. In the new locations, you find that A has no intron but B does. From these facts, what can you conclude about the mechanisms of transposition for the two transposable elements? a. B probably makes a transposase. b. A probably has inverted repeats at each end of the element. c. B probably uses RNA as an intermediate in the transposition event. d. B probably makes a reverse transcriptase. e. A probably doesn’t create a duplication of the host genome target sequence.

Answer 43

a. B probably makes a transposase.

Question 44

A new IS element is found in bacteria. Which of the following pairs of DNA sequences would most likely be found at each end of the IS element? (Only one of the two DNA strands is given.) a. 5´-GAGACTCTAC-3´ and 5´-GAGACTCTAC-3´ b. 5´-GAGACTCTAC-3´ and 5´-CATCTCAGAG-3´ c. 5´-GAGACTCTAC-3´ and 5´-CTCTGAGATG-3´ d. 5´-GAGACTCTAC-3´ and 5´-GTAGAGTCTC-3´ e. 5´-GAGACTCTAC-3´ and 5´-CAGACTCTAG-3´

Answer 44

d. 5´-GAGACTCTAC-3´ and 5´-GTAGAGTCTC-3´

Question 45

1. A transposable element is found to use RNA as an intermediate in transposition. On the basis of this information, which of the following would you expect to be correct? a. The transposable element also probably makes transposase. b. The transposable element may encode a reverse transcriptase. c. The transposable element is probably located in a bacterial genome. d. The transposable element probably contains inverted repeats at each end. e. The transposable element will not be able to transpose without a second copy also present in the genome.

Answer 45

b. The transposable element may encode a reverse transcriptase.

Question 46

Which of the following pairs of sequences would you expect to be found in the same transposable element? a. Inverted repeats and a gene for transposase b. Long terminal repeats and a gene for transposase c. Inverted repeats and a gene for reverse transcriptase d. A gene for transposase and a gene for reverse transcriptase e. Both B and C are both correct.

Answer 46

a. Inverted repeats and a gene for transposase

Question 47

What is the function of DNA glycosylases? a. Recognize and cleave phosphodiester bonds in DNA b. Recognize and remove modified bases from the sugar component of DNA c. Reattach the two parts of DNA that result from double-strand breaks d. Remove pyrimidine dimers from DNA of E. coli that result from exposure to UV light e. Prevent strand slippage during DNA replication

Answer 47

b. Recognize and remove modified bases from the sugar component of DNA

Question 48

Which of the following is a form of direct DNA repair? a. Base-excision repair b. Nucleotide excision repair c. Homologous recombination d. Mismatch repair e. Photoreactivation

Answer 48

e. Photoreactivation

Question 49

Which of the following pairs of DNA repairs systems will repair pyrimidine dimers in E. coli? a. Mismatch repair and base-excision repair b. Photoreactivation and mismatch repair c. Nucleotide-excision repair and base-excision repair d. Photoreactivation and nucleotide-excision repair e. Nonhomologous end joining and nucleotide-excision repair

Answer 49

d. Photoreactivation and nucleotide-excision repair

Question 50

The disorder xeroderma pigmentosum is associated with a defect in what type of DNA repair system? a. Mismatch repair b. Base-excision repair c. Reactivation d. Nucleotide-excision repair e. Homologous recombination

Answer 50

d. Nucleotide-excision repair

Question 51

Which of the following DNA repair systems does not involve the activity of a DNA polymerase? a. Mismatch repair in humans b. Nucleotide-excision repair in yeast c. Photoreactivation in E. coli d. Base-excision repair in E. coli e. All of the above in the activity of a DNA polymerase

Answer 51

c. Photoreactivation in E. coli

Question 52

1. Which of the following enzyme activities is not a part of nucleotide-excision repair? a. DNA polmerase b. DNA ligase c. Reverse transcriptase d. DNA helicase e. All of the above are part of nucleotide-excision repair.

Answer 52

c. Reverse transcriptase

Question 53

]Strains of E. coli that are defective in mismatch repair have very high levels of spontaneous mutagenesis. Studies have shown that in wild-type strains A:C and G:T mispairings (as opposed to the normal A:T and G:C pairings) that occur during DNA replication are more likely than other mispairings (A:G, etc.) to be detected and repaired in these mismatch repair-proficient, wild-type strains. Which of the following types of base substitutions would you expect to be most common among the spectrum of spontaneous mutations created by the mutant mismatch repair-defective strains? a. A-to-C b. C-to-A c. G-to-C d. A-to-G e. A-to-T

Answer 53

d. A-to-G