Ch.16 Mechanisms Of Genetic Variation Test Bank Answers

Prescott's Microbiology, 11e (Willey)

Chapter 16 Mechanisms of Genetic Variation

1) During generalized transduction ________.

A) the host chromosome is degraded into randomly sized fragments

B) any DNA fragment of the appropriate size is packaged

C) any bacterial gene may be transferred to the subsequent host

D) All of the choices are correct.

2) Genes for antibiotic resistance can be found in antibiotic-producing bacteria as well as in non-antibiotic-producing bacteria. 

3) All of the following are appropriate strategies for overcoming drug resistance in bacteria except ________.

A) decreasing the use of antibiotics in agriculture

B) patient compliance with dosage instructions when taking antibiotics

C) heightened infection control in health care facilities

D) prudent use of antibiotics when treating viral infections

4) One strategy to overcome antibiotic resistance is to use the same antibiotics in animal husbandry as those that are prescribed for humans, since the potential for resistant bacteria to evolve would be limited to only a small number of drug classes.

5) Specialized transduction can be carried out by ________.

A) any bacteriophage

B) any temperate bacteriophage

C) only those temperate bacteriophages that integrate into the host chromosome

D) All of the choices are correct.

6) Which of the following is not true of specialized transduction?

A) It is carried out by temperate phage.

B) It is restricted to those genes on either side of an integrated prophage.

C) The phage genome retains the full complement of phage genes.

D) All of the choices are correct.

7) A(n) ________ is a latent form of a virus genome that remains within the host without destroying it.

8) If chromosomal DNA from a host is the only type of DNA carried by a transducing particle, what can be concluded regarding transduction in this case? 

A) Transduction in this case is generalized rather than specialized.

B) Transduction in this case is specialized rather than generalized.

C) Transduction in this case could be generalized or specialized depending on the phage involved.

D) Transduction in this case is neither generalized nor specialized.

9) If chromosomal DNA from a host and phage DNA are carried by a transducing particle, what can be concluded regarding transduction in this case? 

A) Transduction in this case is generalized rather than specialized.

B) Transduction in this case is specialized rather than generalized.

C) Transduction in this case could be generalized or specialized depending on the phage involved.

D) Transduction in this case is neither generalized nor specialized.

10) During specialized transduction carried out by lambda phage in Escherichia coli, differences in the phage and host attachment (att) sites mediate insertion of phage DNA into host DNA.   

11) If the att site of Escherichia coli was dissimilar to that of lambda phage due to a mutation, how would transduction be affected?

A) Phage DNA would be unable to integrate into host DNA.

B) Lambda phage would be unable to package host DNA.

C) Specialized transduction would become generalized.

D) Transduction would not be affected since mutation is only in the host cell.

12) In order to take up a naked DNA molecule, a cell must be ________, which may occur only at certain stages in the life cycle of the organism.

13) A microbiologist is working with two genera of bacteria, A and B, to determine if cells are competent. Strains are grown under optimal conditions, and DNA fragments that carry the gene for green fluorescent protein are added to each culture at 20-minute intervals. Samples from each treatment are plated to nutrient agar and incubated, after which the plates are examined under an ultraviolet lamp. The microbiologist observes that all plates of bacteria B contain colonies that are fluorescent, while for bacteria A only the plates from stationary phase demonstrate fluorescent colonies. What can be concluded from these results?       

A) Both bacteria A and bacteria B cells are competent.

B) Competence in bacteria A is constitutively expressed.

C) Competence in bacteria B is dependent on the phase of growth.

D) Neither bacteria A nor bacteria B cells are competent.

14) A microbiologist is working with a bacteria strain to determine if cells are competent. Cells are grown under optimal conditions with DNA fragments that carry two genes, green fluorescent protein and ampicillin resistance, and then plated to nutrient agar with and without ampicillin. Following incubation, plates are examined for fluorescent colonies under a UV lamp. Predict the results if cells are competent. 

A) Fluorescent colonies will be present on both types of plates.

B) Fluorescent colonies will be present on the ampicillin agar plates, but there will be no growth on the nutrient agar plates.

C) Colonies will be present on both types of plates, but will only fluoresce on the ampicillin agar plates. 

D) There will be no growth on either type of plate.

15) Stable integration of foreign DNA into a bacterial host genome is generally accomplished through induced plasmid transformation than by natural uptake of free DNA fragments. 

16) Which procedure is most associated with unsuccessful transformation and degradation of DNA?

A) Naturally-occurring transformation with DNA fragments in competent bacteria.

B) Induced transformation with plasmid DNA in noncompetent bacteria.

C) Integration of DNA fragments in competent bacteria following naturally-occurring transformation. 

D) Addition of DNA fragments from competent bacteria to live, noncompetent bacteria without artificial induction.

17) The transformation frequency of very competent cells is about 10−6, or about 1 in 1,000,000 when an excess of DNA is used.

18) Competency has been observed in only a limited number of species in nature, but we have found ways to induce the process upon other species in the laboratory.

19) Complete transfer in an Hfr × F− mating takes approximately ________ minutes.

A) 20

B) 50

C) 100

D) 200

20) Predict the outcome of an F+ to F− mating if the F+ cell lacked a functional tra operon. 

A) Upon entering the recipient, the F factor would be unable to integrate into to host chromosome. 

B) Conjugation would not occur because there would be no contact between the F+ and F− cells.

C) Conjugation would occur, but the F- recipient could not become Hfr.

D) There would be no effect on conjugation.

21) When assessing the role of conjugative bacteria in the spread of antibiotic resistance genes, it is fair to say that Hfr cells contribute most while F− cells contribute least. 

22) An Hfr cell and an F− cell result from conjugation between a donor cell and a recipient cell. Which statement is false regarding this event?  

A) The donor could have been either F− or F+.

B) The donor could have been Hfr.

C) The recipient could have been F−.

D) The donor could not have been F−.

23) A cell that is Hfr and a cell that is F+ can be the same cell.

24) Who is credited with demonstrating unidirectional and nonreciprocal transfer of DNA between two mating E. coli cells?

A) Hayes

B) Lederberg

C) Tatum

D) None of the choices are correct.

25) The order of gene transfer in an Hfr × F− mating is best represented by ________.

A) all plasmid genes followed by some or all of the chromosome

B) part of the plasmid followed by the chromosome followed by the rest of the plasmid

C) the chromosome followed by the plasmid

D) part of the chromosome followed by the plasmid followed by the rest of the chromosome

26) When an F' plasmid acts as the donor in a mating, which of the following do(es) not happen?

A) The recipient becomes F'.

B) The plasmid is transferred, including the chromosomal genes now on the plasmid.

C) Some chromosomal genes not on the plasmid are transferred.

D) All of the choices are correct.

27) In an F+ × F− mating, all or part of the host chromosome usually is transferred to the recipient.

28) When an F plasmid integrates into the host chromosome, the strain is referred to as ________.

A) F+

B) Hfr

C) F'

D) F−

29) An F' plasmid results when ________.

A) an F+ × F− mating is interrupted before completion

B) an Hfr × F− mating is interrupted before completion

C) an integrated F plasmid is incorrectly excised, bringing host genes with it

D) None of the choices are correct.

30) In the mechanics of conjugation, exclusive of gene transfer, Hfr and F+ strains behave the same.

31) A plasmid that can either exist independently of the chromosome or be integrated into it is called a(n) ________.

32) In an Hfr × F− mating, the conjugation bridge usually breaks before chromosomal transfer is complete. Therefore, the recipient remains F−.

33) Plasmids that have genes that decrease bacterial susceptibility to antibiotics are called ________ factors.

A) col

B) resistance

C) virulence

D) metabolic

34) The conjugation bridge in an Hfr × F− mating usually breaks before chromosome transfer is complete; however, because at least part of the plasmid is transferred first, the recipient becomes F+.

35) A ________ is a piece of extrachromosomal DNA that has its own replication origin.

36) Following an F+ × F− mating, the donor is ________ and the recipient is ________.

A) F+; F−

B) F−; F+

C) F−; F−

D) F+; F+

37) In an F+ × F− conjugation, the donor is the ________ strain.

A) F+

B) F−

C) both F+ and F− (it is a reciprocal exchange)

D) neither F+ nor F− (there is no exchange)

38) Plasmids that have genes for pili and can transfer copies of themselves to other bacteria during conjugation are called ________ plasmids.

39) Conjugative transposons ________.

A) can be transferred from one bacterium to another by a phage-mediated process

B) may be involved in the spread of antibiotic resistance in bacteria

C) often express enzymes that degrade aromatic compounds

D) All of the choices are correct.

40) An insertion sequence is distinguishable from other mobile genetic elements because ________.

A) it is smallest

B) it encodes a transposase

C) it is highly complex

D) it is composed of DNA

41) A transposable element composed of an antibiotic resistance gene, a recombinase gene, and inverted repeats is identified in a bacterial genome.  This element can be any of the following except ________.

A) an insertion sequence

B) a composite transposon

C) a unit transposon

D) an integrated conjugative element

42) Insertion sequences are ________.

A) normally relatively short (700 to 1,650 bp)

B) capable of transposition

C) are discrete genetic elements bounded at both ends with inverted repeats

D) All of the choices are correct.

43) Transposons that insert at a new location while a copy remains at the original location are said to mediate ________ transposition.

A) simple

B) composite

C) incomplete

D) replicative

44) Which of the following conclusions can be made if two identical insertion sequences are identified in separate locations on a chromosome?

A) The insertion sequence was transferred via replicative transposition.

B) The insertion sequence was a "cut-and-paste" transposon.

C) The insertion sequence was transferred via simple transposition.

D) A mutation occurred during transposition of the insertion sequence.

45) Transposable elements have been found only in bacteria and do not appear to play a major role in eukaryotes.

46) Which of the following effects may be mediated by transposable elements?

A) A mutation may result from insertion into a gene.

B) Activation of nearby genes may occur.

C) Genetic deletions may form.

D) All of the choices are correct.

47) Which of these transposable elements do not carry genes for functions other than those needed for transposition?

A) Insertion sequences

B) Composite transposons

C) Retrotransposons

D) Conjugal transposons

48) When a recipient cell acquires a piece of naked DNA from the environment, it is called ________.

A) conjugation

B) transformation

C) transduction

D) transfection

49) If one reproductive strategy of a eukaryotic organism is gamete fusion, what can be concluded about that organism? 

A) The organism participates in vertical gene transfer.

B) The organism participates in horizontal gene transfer.

C) The organism reproduces asexually.

D) Progeny organisms are identical to each other.

50) Which of the following methods of genetic recombination is common to both eukaryotic and bacterial cells?

A) Vertical gene transfer

B) Crossing over 

C) Gamete fusion

D) All of the choices are correct.

51) Which statement best summarizes the major distinction between horizontal gene transfer and vertical gene transfer? 

A) The recipient of genes in horizontal transfer is a mature cell, whereas the recipient of genes in vertical transfer is a progeny cell.

B) Horizontal transfer is observed in bacteria and archaea, whereas vertical transfer is observed in all cells. 

C) Organisms that use horizontal transfer can only reproduce asexually, whereas organisms that use vertical transfer can reproduce sexually or asexually.

D) Genes are more stable in recipient cells following horizontal transfer that in those following vertical transfer.

52) Bacterial isolates from post-surgical infections of several patients on the same hospital floor demonstrate an increase in resistance to similar antibiotics. The pattern of antibiotic resistance in these cases is most likely due to vertical gene transfer among bacteria that carry resistance genes to bacteria that lack those genes.

53) The process in which one or more nucleic acid molecules are rearranged or combined to produce a new nucleotide sequence is called ________.

A) transformation

B) conjugation

C) recombination

D) transduction

54) Site-specific recombination systems ________.

A) do not depend on extensive nucleotide sequence homology

B) depend on enzymes that are often specific for sequences within the host

C) are features of some viruses

D) All of the choices are correct.

55) A reciprocal exchange in which two DNA molecules with the same nucleotide sequence break and rejoin in a crossover is called ________ recombination.

A) homologous

B) site-specific

C) replicative

D) None of the choices are correct.

56) The incorporation of a single strand of donor DNA into a recipient DNA duplex so that the donor strand replaces one of the strands or the recipient duplex generates ________ DNA.

A) aberrant

B) unstable

C) heterogeneous

D) heteroduplex

57) A DNA molecule that enters a bacterium by one of several mechanisms is called a(n) ________.

A) merozygote

B) exogenote

C) endogenote

D) None of the choices are correct.

58) The genome of a recipient cell is called a(n) ________.

A) merozygote

B) exogenote

C) endogenote

D) None of the choices are correct.

59) A recipient cell that is temporarily diploid for a portion of the genome during the replacement process is called a(n) ________.

A) merozygote

B) exogenote

C) endogenote

D) None of the choices are correct.

60) When bacterial genes are transferred to another bacterium by a virus, it is called ________.

A) conjugation

B) transformation

C) transduction

D) transfection

61) Which of the following is true of the integration of a viral genome into the host chromosome?

A) Integration of the viral genome is a form of site-specific recombination.

B) The enzymes that are used in integration are nonspecific for the virus and its host.

C) Integration begins the process of host chromosome degradation.

D) All of the choices are correct.

62) One possible fate for an exogenote is ________.

A) integration into the host chromosome

B) independent replication and functioning

C) degradation to nucleotides

D) All of the choices are correct.

63) Transfer of genes from one mature independent organism to another is called ________.

A) horizontal gene transfer

B) lateral gene transfer

C) vertical gene transfer

D) orthogonal gene transfer

64) Host ________ is the process by which some cells are able to degrade an exogenote.

65) In mismatch repair on newly replicated DNA, enzymes distinguish between old and newly replicated DNA strands based on the fact that newly replicated DNA strands are ________-methylated relative to older DNA.

66) If you wished to study the SOS response in Escherichia coli, which of the following experimental procedures could be used? 

A) Expose cells to nonionizing radiation for 20 minutes.

B) Expose cells to ionizing radiation for 10 minutes.

C) Transfer log phase cells from complete medium to thymine minimal medium.

D) Inactivate genes that encode DNA polymerases.

E) All of the choices are correct.

67) What would be the hypothetical outcome if the action of RecA was inhibited during the SOS response?

A) LexA would not autolyse, and therefore the transcription of DNA repair genes would not occur.

B) LexA would autolyse, and therefore the transcription of DNA repair genes would occur.

C) LexA would autolyse, and therefore the transcription of repair genes would not occur.

D) LexA would not autolyse, and therefore the transcription of repair genes would occur.

68) Photoreactivation repairs thymine dimers by splitting them back into separate thymines.

69) Repair of an apurinic or apyrimidinic site in DNA by AP endonuclease must be completed by the action of ________.

A) UvrABC endonuclease

B) RecA protein

C) DNA polymerase I

D) None of the choices are correct.

70) Which of the following is the most error-prone of the repair mechanisms?

A) Postreplication repair

B) Recombination repair

C) SOS repair

D) Photoreactivation

71) Repair of thymine dimers using light to split the dimers apart into separate monomers is called ________.

A) photodedimerication

B) photoreactivation

C) photoreparation

D) None of the choices are correct.

72) SOS repair ________.

A) requires RecA protein

B) is inducible by DNA damage

C) is error prone, i.e., produces mutations

D) All of the choices are correct.

73) Microbial strains that can grow on minimal medium are called ________.

A) autotrophs

B) auxotrophs

C) prototrophs

D) minitrophs

74) A public health microbiologist plans to screen a particular bacterial species that was isolated from several patients in an intensive care unit to detect if any of the cells are penicillin-resistant mutants. What is the first step in conducting this experiment?

A) Determine whether or not wild type cells of the same bacterial species are susceptible to penicillin.

B) Test the cells to see if they can grow on media to which penicillin has been added.

C) Perform an antibiotic susceptibility test on the cells using antibiotics other than penicillin that are known to be effective.

D) Set up an Ames test to see if any of the isolates are mutagenic.

75) To best isolate mutant bacteria that are threonine auxotrophs from a larger population, threonine-rich media should be inoculated and any colonies that form are presumptive auxotrophic mutants.

76) Which type of medium support growth of mutant bacteria that are threonine auxotrophs?

A) Threonine auxotrophs only grow on media that is supplemented with threonine.

B) Threonine auxotrophs only grow on media that lacks threonine.

C) Since threonine is essential for growth, threonine auxotrophs do not grow on any type of media.

D) Since threonine is essential for growth, threonine auxotrophs can grow on any type of media.

77) What type of procedure is appropriate to isolate revertants from a population of threonine auxotrophic cells? 

A) Grow the auxotrophic cells on an agar plate without threonine; any colonies that form are presumed revertant.

B) Grow the auxotrophic cells on and agar plate with threonine; any colonies that form are presumed revertant.

C) Grow the auxotrophic cells in broth with threonine; if the broth becomes cloudy, revertants are presumed present.

D) Threonine auxotrophic revertants could not be isolated on any type of media.

78) Which type(s) of mutation might lead to a threonine auxotrophic revertant?

A) Base substitution

B) Missense mutation

C) Point mutation

D) All of the choices are correct.

79) ________ are strains that are unable to grow on a minimal medium that supports growth of the wild type strain, but are able to grow on the minimal medium if one or more nutritional supplements are added.

A) Autotrophs

B) Auxotrophs

C) Prototrophs

D) Minitrophs

80) The Ames test ________.

A) can be used to measure the mutagenicity of chemicals

B) is used to measure the repair of thymine dimers

C) is used to measure levels of oxygen-free radicals

D) None of the choices are correct.

81) Approximately half of known animal carcinogens can be detected by the Ames test.

82) The ________ ________ is the most prevalent form of a gene in a population.

83) ________ are physical or chemical agents that cause mutation.

84) If a region of DNA contained numerous mismatches due to a modifying agent that caused methylation of guanine, which of the following mutagens is most likely the cause? 

A) A deaminating base such as nitrous oxide

B) An intercalating agent such as acridine orange

C) A DNA modifier such as an alkylating agent

D) Ionizing energy such as gamma radiation

85) Acridine orange is a purine base analogue.

86) Which of the following mutagens is most different than the others in terms of its effect on DNA?

A) Acridine orange

B) Intercalating agent

C) Planar mutagen that inserts between stacked bases

D) Base analogue

87) If 5-bromouracil was added to a culture of actively dividing bacterial cells, resulting mutations could eventually become a stable part of the cellular genome.

88) A microbial geneticist observes that a significant number of pyrimidine dimers are present in bacterial DNA following exposure to a particular mutagen. To which mutagen were the bacterial cells likely exposed?

A) UV light

B) Acridine orange

C) 5-bromouracil

D) X-rays

89) A change in genotype, but not in phenotype, is most likely due to ________.

A) a nonsense mutation at the beginning of a gene

B) a point mutation in the third position of a DNA triplet

C) a mutation that leads to a frameshift in the middle of a gene

D) thymine dimer formation in the coding region of a gene

90) Predict the outcome of protein synthesis if a gene undergoes a mutation in its anticodon region where a charged tRNA recognizes a nonsense mutation.  

A) Transcription and translation both would continue.

B) Transcription would continue but translation would not continue.

C) Transcription and translation both would not continue.

D) Transcription would not continue but translation would continue.

91) Lethal mutations can be maintained in diploid organisms if they are ________.

A) dominant

B) recessive

C) deletions

D) None of the choices are correct.

92) Mutations that result in the death of an organism when expressed are called ________ mutations.

A) dominant

B) recessive

C) lethal

D) conditional

93) Alternate forms of genes resulting from mutations are called ________.

A) isoforms

B) alterons

C) alleles

D) lethal

94) A mutation from the most prevalent form of a gene to a mutant form is called a ________ mutation.

A) forward

B) reverse

C) wild card

D) escalating

95) A mutagen that inserts between the stacked bases of a DNA double helix, distorting the DNA to induce single-pair insertions or deletions is called a(n) ________ agent.

A) insertional

B) interspersing

C) intercalating

D) distortional

96) By definition, if the DNA of a cell undergoes a spontaneous mutation, is was NOT due to ________.

A) errors in DNA replication

B) insertion of transposons

C) exposure to radiation

D) spontaneous depurination of nucleotides

97) A ________ mutation does not alter the amino acid sequence of the resulting protein.

A) missense

B) nonsense

C) silent

D) None of the choices are correct.

98) As the result of exposure to a mutagen, cytosine is substituted for thymine in one strand of DNA. Upon subsequent DNA replication, one of the daughter cells will have a GC pair in this position instead of an AT pair. This is called a(n) ________ mutation.

A) transversion

B) transition

C) frameshift

D) insertion

99) Transition mutations can result from ________.

A) incorporation of a base analog that exhibits different base-pairing properties from the base it replaces

B) chemical modification of an existing base in the DNA so that in the next round of replication it will pair differently from the unmodified base

C) incorporation of a base analog that exhibits different base-pairing properties from the base it replaces and chemical modification of an existing base in the DNA so that in the next round of replication it will pair differently from the unmodified base

D) a small insertion or deletion

100) Which of the following is considered a reverse mutation that will restore the wild type phenotype?

A) True reversion back to the wild type base sequence

B) Mutation to a different base sequence, but one that restores the amino acid sequence in the protein to the wild type sequence

C) A mutation that restores the function of a protein, even though it does not restore the base sequence or the amino acid sequence to the wild type

D) All of the choices are correct.

101) Which of the following types of mutation may play an important role in driving evolution because they are often nonlethal and, therefore, remain in the gene pool?

A) Nonsense

B) Missense

C) Frameshift

D) Deletion

102) A mutation that changes the amino acid sequence of the resulting protein by substitution is called a ________ mutation.

A) missense

B) nonsense

C) silent

D) None of the choices are correct.

103) Lethal mutations can be recovered in bacteria if they are ________.

A) dominant

B) active

C) conditional

D) None of the choices are correct.

104) A ________ mutation is one that causes premature termination of the synthesis of the protein product.

A) missense

B) nonsense

C) silent

D) None of the choices are correct.

105) ________ mutations affect only a single base pair in a gene.

106) Mutations resulting from exposure to physical or chemical agents are called ________ mutations.

107) ________ mutations occur in the promoter or operator region of a gene or set of genes and affects the expression of the downstream genes without affecting the amino acid sequences of the gene products.

108) Transfer of genetic information via direct cell-cell contact is called ________.

A) transformation

B) transduction

C) transfection

D) conjugation

109) Which of the following statements is false regarding the consequences of horizontal gene transfer?

A) Horizontal gene transfer is the main mechanism that drives the evolution of microorganisms.

B) Horizontal gene transfer allows microbes to better survive environmental stresses such as UV radiation by replacing their own damaged DNA with intact DNA from another organism.

C) Genetic changes resulting from horizontal gene transfer affects the virulence of bacteria when pathogenicity islands are transferred between organisms.

D) Microbes can expand their ecological niche when horizontal gene transfer bestows beneficial traits such as antibiotic resistance.

E) Horizontal gene transfer allows the donor DNA to self replicate, simultaneously repressing reproduction in the recipient.

110) Homologous recombination differs from site-specific recombination in that ________.

A) homologous recombination involves long stretches of similar-sequence nucleotides on two DNA molecules that break and reanneal in a crossover mechanism, whereas site-specific recombination occurs at target sites, catalazed by recombinases

B) homologous recombination takes place at specific target sites catalazed by recombinases, whereas site-specific recombination involves long stretches of same-sequence nucleotides on two DNA molecules that break and reanneal in a crossover mechanism

C) homologous recombination takes place in eukaryotic cells during meiosis, whereas site-specific recombination takes place in bacteria and archaea during horizontal gene transfer

D) homologous recombination utilizes enzymes collectively called recombinases, whereas site-specific recombination involves RecA to bring about the crossover between DNA molecules

111) Mobilizable genomic islands (MGIs) differ from integrative conjugative elements (ICEs) in that ________.

A) MGIs include an att site, allowing large portions of the bacterial chromosome to be transferred, whereas ICEs are transposons in nature

B) MGIs are insertion sequences, whereas ICEs are transposons

C) MGIs are transferred by conjugation, whereas ICEs are transferred by transduction

D) MGIs transfer pathogenicity islands, whereas ICEs transfer antibiotic-resistance genes