Chapter 6 - Genetic Analysis and Mapping in Bacteria and Bacteriophages

1) Which of the following is false regarding plasmids?

A) They are small double stranded circular DNA molecules.

B) They contain essential genes for metabolism.

C) They can have genes that promote their own transfer from one bacterium to another.

D) They can carry genes for antibiotic resistance.

E) They generally replicate autonomously.

B) They contain essential genes for metabolism.

2) Which of the following is true of a bacterial strain that is his+ lac+ gal- ampR.

A) It is auxotrophic for histidine.

B) It will grow on ampicillin.

C) It is unable to synthesize histidine.

D) It can use galactose as an energy source.

E) It is unable to break down lactose.

B) It will grow on ampicillin.

**3) A lab technician has four strains of bacteria. Although he forgot to label them, he knows that they include one F+ strain, one Hfr strain, one F' strain, and one F- strain. He observed the following results after plating these strains on different media. Which of the following plates can be used to identify the F- strain?

A) complete media

B) minimal media with histidine, glutamate, and cysteine

C) minimal media with histidine, glutamate, cysteine, and streptomycin

D) minimal media with streptomycin

E) minimal media with leucine and streptomycin

C) minimal media with histidine, glutamate, cysteine, and streptomycin

4) Which of the following is incorrect about genetic analysis and mapping in bacteria and bacteriophages?

A) Conjugation requires cell-to-cell contact.

B) Generalized transduction uses lytic phage and specialized transduction uses a lysogenic phage.

C) Transformation requires a vector to carry donor DNA fragments to the recipient cell.

D) Conjugation, transformation, and transduction all require recombination.

E) Conjugation, transformation, and transduction can all be used to map the order of genes on a bacterial chromosome.

C) Transformation requires a vector to carry donor DNA fragments to the recipient cell.

5) Why does conjugation with an Hfr donor result in a much higher rate of gene transfer than conjugation with an F+ donor?

A) An F+ donor makes fewer pili.

B) An F+ donor's T strand is slow to reach the pilus.

C) The Hfr donor transfers genes from the chromosome and not the plasmid.

D) The Hfr donor segment must undergo recombination in the recipient.

E) The F+ donor segment must undergo recombination in the recipient.

C) The Hfr donor transfers genes from the chromosome and not the plasmid.

6) Which of the following is NOT a step involved in rolling circle replication during conjugation?

A) Replication begins at the oriT after relaxosome binding.

B) Relaxase facilitates passage of the T strand into the recipient cell.

C) A protein complex known as the relaxosome cuts one strand of the F+ plasmid.

D) A double stranded plasmid is transferred to the F- cell through the conjugation pilus.

E) Rolling circle replication occurs in the donor.

D) A double stranded plasmid is transferred to the F- cell through the conjugation pilus.

7) When F+ conjugation occurs successfully, only one copy of the F plasmid single-stranded DNA is transferred. What else must minimally occur?

A) circularization of the recipient's new DNA

B) circularization plus replication of the new recipient DNA

C) stopping the rolling circle replication after one copy length, circularization, and replication

D) continuation of rolling circle replication in the donor cell and replication in the recipient cell

E) rolling circle replication in the recipient cell

C) stopping the rolling circle replication after one copy length, circularization, and replication

8) Which of the following is an accurate statement regarding F factor states?

A) An F+ cell can convert exconjugants to a donor state, as well as change their genotype.

B) An Hfr cell can convert exconjugants to a donor state, as well as change their genotype.

C) An F' cell can convert exconjugants to a donor state, as well as change their genotype.

D) F+ and Hfr cells cannot convert exconjugants to a donor state.

E) F+ and F' cells cannot transfer donor genes to exconjugants.

C) An F' cell can convert exconjugants to a donor state, as well as change their genotype.

**(9) In the flow diagram shown below, which of the following is an inaccurate relationship between bacterial strains in the various F factor states?

A) Link 1 represents transfer of an entire F plasmid.

B) Link 2 represents integration of the F plasmid into the host chromosome.

C) Link 3 represents precise excision of the F plasmid from the chromosome.

D) Link 4 represents excision of the F plasmid plus some host DNA from the chromosome.

E) All four links represent accurate relationships.

E) All four links represent accurate relationships.

10) To map genes of a bacterial strain, conjugation must be interrupted at given times. Suppose you have Hfr cells of genotype a+b+c+d+e+strR and F- cells of genotype a-b-c-d-e-strS and you combine these two cultures in liquid medium in four blenders at time 0. After intervals of 3, 6, 9, and 12 minutes, you turn on successive blenders. What role does the blender play in the experiment?

A) serves as a culture container only

B) acts as a mechanism to bring cells into contact

C) speeds up molecular movement of DNA

D) shears the sex pili of conjugants

E) hastens conjugation events

D) shears the sex pili of conjugants

11) To map genes of a bacterial strain, conjugation must be interrupted at given times. Suppose you have Hfr cells of genotype a+b+c+d+e+strR and F- cells of genotype a-b-c-d-e-strS and you combine these two cultures in liquid medium in four blenders at time 0. After intervals of 3, 6, 9, and 12 minutes, you turn on successive blenders. The resulting cultures were then plated on medium containing streptomycin. Why?

A) to eliminate non-conjugating Hfr cells

B) to eliminate all non-conjugated cells

C) to eliminate non-conjugated F- cells

D) to selectively eliminate cells that have taken in F+ genes

C) to eliminate non-conjugated F- cells

**12) To map genes of a bacterial strain, conjugation must be interrupted at given times. Suppose you have Hfr cells of genotype a+b+c+d+e+strR and F- cells of genotype a-b-c-d-e-strS and you combine these two cultures in liquid medium in four blenders at time 0. After intervals of 3, 6, 9, and 12 minutes, you turn on successive blenders. The graph below shows the results of plating the cultures from each blender. What is the correct order of the genes on this chromosome?

A) a b c d e

B) a c e b d

C) b e c a (d is unknown)

D) d a c e b

E) b e c a d

B) a c e b d

13) Which of the following allows the compilation of time-of-entry maps?

A) the use of many replicates of each experiment

B) the use of appropriate controls repeatedly

C) the fact that gene entry can proceed in either direction

D) the observation that Hfr genes recombine so efficiently

E) the recognition of phenotype interaction

C) the fact that gene entry can proceed in either direction

14) In five Hfr strains, each of which was used to build a time-of-entry map, the genes entered the recipient cells as follows:

Strain 1: S L A C T F

Strain 2: N P F T C A

Strain 3: T F P N U Y

Strain 4: S H Y U N P

Strain 5: U N P F T C

Which of the following represents a correct compilation of these results

A) S L A C T F P N H C U

B) N P F T S L A C H U T

C) T C A L S P N U Y H

D) U N P F T C A L S T F

E) S L A C T F P N U Y H

E) S L A C T F P N U Y H

15) An F′ donor includes F DNA plus a segment of bacterial chromosome DNA. If conjugation is interrupted before the entire F′ chromosome transfers, what could be the expected consequences?

A) integration of some but not all F′ genes into the recipient's chromosome

B) a smaller F′ plasmid than had been present in the donor

C) failure of the F′ strand to circularize in the recipient

D) change of the recipient from F- to F+

E) formation of a recipient that is a stable partial diploid

C) failure of the F′ strand to circularize in the recipient

***16) Jacob and colleagues developed a time-of-entry mapping technique. They used the genes for threonine and leucine synthesis (thr and leu), which are near the oriT site, as selected markers. Additionally, they used an E. coli F- strain P678 that has dysfunctional variants for all of the genes studied. They also used an HfrH strain that carried a functional allele for all genes studied. Which of the following statements is FALSE regarding the time-of-entry profile they acquired?

A) Had the experiment continued, a time of entry map could be viewed for the entire E. coli chromosome.

B) The azi gene is closer to the thr and leu genes than the ton, lac, and gal genes.

C) The ton gene is found between the azi and lac genes.

D) The lac+ allele appears at about 16 or 17 minutes.

E) At 40 minutes, nearly 20% of exconjugants screened for the selected markers have the gal+ allele.

A) Had the experiment continued, a time of entry map could be viewed for the entire E. coli chromosome.

17) Which of the following is NOT a step in transformation?

A) Donor cell DNA binds to a receptor site on the recipient cell.

B) The donor cell lyses, releasing pieces of its chromosome into the environment.

C) Both strands of the donor cell DNA are degraded.

D) DNA fragments pair with homologous regions of the recipient cell chromosome.

E) DNA recombines with the recipient cell chromosome.

C) Both strands of the donor cell DNA are degraded.

18) A competent bacterial strain with genes a, b, and c is transformed by a donor bacterial fragment. Cotransformation frequencies for each gene pair are as follows:

a and b 0.04%

a and c 0.02%

b and c 0.0064%

Which conclusion can be definitively made from this data?

A) Genes b and c are farthest apart.

B) Gene order is a, b, then c.

C) Gene a is closer to c than to b.

D) Gene b is closer to c than to a.

E) Cotransformation of b and c is so frequent, they must be one gene.

A) Genes b and c are farthest apart.

19) Which of the following statements about the T4 lytic life cycle is false?

A) The host DNA breaks down.

B) Under the direction of phage genes, transcription and translation produce new phage components.

C) Progeny phage particles are released by lysis from host bacteria.

D) The phage DNA is injected into the host.

E) The phage DNA is integrated into the host chromosome.

E) The phage DNA is integrated into the host chromosome.

20) In generalized transduction, a phage introduces a segment of donor DNA into the recipient cell. This is followed by recombination of the donor fragment with the recipient chromosome. Which of the following must occur?

A) circularization of the donor fragment before recombination

B) a pair (or even number) of crossovers between the donor segment and the recipient

C) degradation of one of the two strands of phage genome

D) replication of the donor segment before recombination

E) a single crossover between the donor segment and the recipient chromosome

B) a pair (or even number) of crossovers between the donor segment and the recipient

21) In a cotransduction experiment the alleles a+, b+, and c+ were studied. The allele a+ alone was transduced into an auxotroph 1750 times, b+ alone 1700 times, and c+ alone 1725 times. Alleles a+ and b+ were both found 11 times, b+ and c+ 117 times, and a+ and c+ 15 times. What can you definitely conclude?

A) The genes are all located extremely close to each other.

B) The gene order is a, b, c.

C) Genes a and b are more closely linked than a and c or b and c.

D) Genes b and c are found together only if double crossovers have occurred.

E) Genes b and c are more closely linked than a and b or a and c.

E) Genes b and c are more closely linked than a and b or a and c.

22) Which of the following statements regarding cotransduction mapping experiments is false?

A) A high co-transduction frequency between two genes is evidence of linkage.

B) A low co-transduction frequency between two genes is evidence of linkage.

C) A selected marker screen identifies transductants for a donor allele of interest.

D) An unselected marker screen identifies transductants for an additional donor allele of interest.

E) Selection identifies transductants that have acquired an even number of crossovers.

B) A low co-transduction frequency between two genes is evidence of linkage.

23) A scientist is setting up a co-transduction experiment to determine the order of five genes in an operon. What gene should be used as the selected marker and what type of media should be used to select for it?

A) a nearby essential metabolic gene upstream of the operon; complete media

B) a nearby essential metabolic gene upstream of the operon; minimal media supplemented with the corresponding essential metabolite

C) a nearby essential metabolic gene downstream of the operon; complete media

D) the first gene in the operon; complete media

E) the first gene in the operon; minimal media supplemented with the corresponding essential metabolite

B) a nearby essential metabolic gene upstream of the operon; minimal media supplemented with the corresponding essential metabolite

**24) A competent bacterial strain that has the genotype a- b- c+ is transduced with a P1 phage carrying a fragment of donor chromosome with the a+ b+ c- alleles. The following number of transductants were found after screening for the selectable marker a+.

Which of the following conclusions is false?

A) The transduction frequency between a and b is 82%.

B) The transduction frequency between a and c is 48%.

C) Gene a and gene b are closer together than gene a and gene c.

D) The gene order is acb.

E) The selected marker screen will inhibit growth of transductants with the genotype a- b+ c-.

D) The gene order is acb.

25) Which methods did Seymour Benzer use to study 20,000 mutants of the rII region of the T4 bacteriophage?

A) genetic complementation analysis only

B) intragenic recombination analysis only

C) deletion-mapping analysis only

D) intragenic recombination analysis and deletion-mapping analysis only

E) genetic complementation analysis, intragenic recombination analysis, and deletion-mapping analysis

E) genetic complementation analysis, intragenic recombination analysis, and deletion-mapping analysis

26) Seymour Benzer found which of the following while studying 20,000 mutants of the rII region of the T4 bacteriophage?

A) Simultaneous infection of rII phage mutants resulted in T4 plaques when the mutations were in the same rII gene.

B) Intragenic recombination analysis could determine the distance between rIIA and rIIB.

C) Intragenic recombination between mutants with partial deletions and point mutations could be used to map the position of individual rII mutations.

D) Deletion-mapping analysis found that a point mutation and a deletion mutation whose locations overlapped resulted in wild-type intragenic recombinants.

E) The size of the plaques on E. coli lawns determined the distance between rIIA and rIIB.

C) Intragenic recombination between mutants with partial deletions and point mutations could be used to map the position of individual rII mutations.

27) Benzer's analysis of phage genomes included deletion mapping. Since recombination could not occur in the area of a deletion, an infection by two phage strains, one of which has a deletion and the other a point mutation, that results in no wild-type recombinants being produced indicates ________.

A) that the deletion includes the position of the point mutation in the same gene

B) that the deletion includes the position of the point mutation in a different gene

C) that the point mutation is dominant

D) that the point mutation is recessive

E) the distance between the two types of mutation

A) that the deletion includes the position of the point mutation in the same gene

29) In his analysis of rII in phage, Benzer assayed complementation. Suppose you try your hand at this with several mutants and get the following results (+ = complementation):

42 and 62 +

42 and 83 -

62 and 63 -

62 and 74 +

42 and 74 -

42 and 75 +

62 and 75 -

What can you conclude?

A) Mutations 42 and 75 are in the same gene.

B) Mutations 62 and 74 are in the same gene.

C) Mutations 62, 63, and 74 are in the same gene.

D) Mutations 42 and 74 are in the same gene.

E) Mutation 63 is not in the same gene as either 62 or 42.

D) Mutations 42 and 74 are in the same gene.

30) Which of the following regarding lateral gene transfer is false?

A) It may occur by conjugation, transformation, or transduction.

B) It facilitates rapid genome evolution.

C) It can convert benign bacteria into pathogens that cause disease.

D) It allows an organism to rapidly acquire whole segments of chromosomes containing multiple genes.

E) It increases the efficiency of antibiotics against normally sensitive strains.

E) It increases the efficiency of antibiotics against normally sensitive strains.

1) One kind of plasmid in bacteria is called an R plasmid. What kinds of genes are typically present on such plasmids?

antibiotic-resistant genes, heavy metal resistance

2) What is the difference between F+ and F- bacteria?

F+ bacteria have an F plasmid.

3) In a bacterial cross of an Hfr donor a+b+ with a recipient F- a-b-, what would be a possible recombinant?

a+b-, a-b+, or a+b+

4) All three types of bacterial recombination share one characteristic. What is it?

one-way transfer of gene(s), or transfer from donor to recipient

What is the role of the relaxosome in conjugation?

binds to F origin, or cleaves T strand, or binds to 5′ end to begin transfer

6) In conjugation, as the 5′ end of the T strand begins to move across the pilus, what form of replication occurs in the donor cell?

rolling circle

7) In Hfr transfer, what happens to linear DNA that does not recombine with the host chromosome?

degradation

8) In an E. coli conjugation experiment, the donor cell is found to be thr+, leu+, his+, and the F- cell is thr-, leu-, and his-. When the mating is interrupted after 10 minutes and the recipients are plated, they are found to be leu+ and his+ but thr-. What can you conclude?

leu and his are close together.

9) In a conjugation experiment, the Hfr donor is thr+, leu+, his+, strR. The recipient is thr-, leu-, his-, strS. Why would you use medium containing streptomycin to analyze your results?

to identify strR recipients

10) If conjugation occurs with an F′ donor, how will the recipient be characterized genetically?

partially diploid

11) What characterizes a bacterial cell that can undergo transformation?

competence, or ability to take up double-stranded DNA

12) What distinguishes generalized versus specialized transduction?

generalized uses lytic phage, specialized uses lysogenic phage

13) Name the two cycles in which bacteriophages act when they infect bacteria.

lysis and lysogeny

14) Seymour Benzer's fine structure studies of genomes used mutations found in specific regions of what kind of genome?

bacteriophage (phage)

15) What is the difference between the revertible and nonrevertible rII mutants that Benzer generated?

revertible mutants were caused by DNA base-sequence substitutions (point mutations) and nonrevertible mutants were caused by partial deletion mutations

1) Bacteria that can grow on minimal medium are called ________ while bacteria that can require one or more essential compounds for growth are called ________.

prototrophs, auxotrophs

2) Some bacteriophages can be either lytic or lysogenic. These are called ________ phages.

temperate

3) Once a phage genome has become part of the host chromosome, it is called a ________.

prophage