Deck 6: Genetic Analysis and Mapping in Bacteria and Bacteriophage

Question 1

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) b e c a d
C) a c e b d
D) d a c e b
E) b e c a (d is unknown)

Answer 1

C

Question 2

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? $$\begin{array} { | l l l l l l | } \hline \text { strain } & \text { his } & g \text { gu } & \text { cys } & \text { leu } & \text { str } \\\mathrm { F } ^ { + } & + & + & + & - & + \\\mathrm { Hfr } & + & + & + & + & - \\\mathrm { F } ^ { \prime } & + & + & + & + & - \\\mathrm { F } & - & - & - & + & + \\\hline\end{array}$$

A) minimal media with leucine and streptomycin
B) minimal media with histidine, glutamate, and cysteine
C) minimal media with histidine, glutamate, cysteine, and streptomycin
D) complete media
E) minimal media with streptomycin

Answer 2

minimal media with histidine, glutamate, cysteine, and streptomycin

Question 3

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

Answer 3

C

Question 4

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

A) It is unable to synthesize histidine.
B) It is auxotrophic for histidine.
C) It is unable to break down lactose.
D) It will grow on ampicillin.
E) It can use galactose as an energy source.

Question 5

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) a smaller F' plasmid than had been present in the donor
B) change of the recipient from F- to F+
C) formation of a recipient that is a stable partial diploid
D) integration of some but not all F' genes into the recipient's chromosome
E) failure of the F' strand to circularize in the recipient

Question 6

Which of the following is false regarding plasmids?

A) They can have genes that promote their own transfer from one bacterium to another.
B) They contain essential genes for metabolism.
C) They can carry genes for antibiotic resistance.
D) They generally replicate autonomously.
E) They are small double stranded circular DNA molecules.

Question 7

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) degradation of one of the two strands of phage genome
B) circularization of the donor fragment before recombination
C) a single crossover between the donor segment and the recipient chromosome
D) a pair (or even number) of crossovers between the donor segment and the recipient
E) replication of the donor segment before recombination

Question 8

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

A) A protein complex known as the relaxosome cuts one strand of the F+ plasmid.
B) A double stranded plasmid is transferred to the F- cell through the conjugation pilus.
C) Rolling circle replication occurs in the donor.
D) Replication begins at the oriT after relaxosome binding.
E) Relaxase facilitates passage of the T strand into the recipient cell.

Question 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 4 represents excision of the F plasmid plus some host DNA from the chromosome.
C) Link 3 represents precise excision of the F plasmid from the chromosome.
D) Link 2 represents integration of the F plasmid into the host chromosome.
E) All four links represent accurate relationships.

Question 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. The resulting cultures were then plated on medium containing streptomycin. Why?

A) to eliminate non- conjugating Hfr cells
B) to selectively eliminate cells that have taken in F+ genes
C) to eliminate non- conjugated F- cells
D) to eliminate all non- conjugated cells

Question 11

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

A) circularization plus replication of the new recipient DNA
B) circularization of the recipient's new DNA
C) rolling circle replication in the recipient cell
D) continuation of rolling circle replication in the donor cell and replication in the recipient cell
E) stopping the rolling circle replication after one copy length, circularization, and replication

Question 12

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

A) the recognition of phenotype interaction
B) the fact that gene entry can proceed in either direction
C) the use of many replicates of each experiment
D) the observation that Hfr genes recombine so efficiently
E) the use of appropriate controls repeatedly

Question 13

Which of the following is NOT a step in transformation?

A) Donor cell DNA binds to a receptor site on the recipient cell.
B) DNA fragments pair with homologous regions of the recipient cell chromosome.
C) The donor cell lyses, releasing pieces of its chromosome into the environment.
D) DNA recombines with the recipient cell chromosome.
E) Both strands of the donor cell DNA are degraded.

Question 14

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) shears the sex pili of conjugants
B) serves as a culture container only
C) acts as a mechanism to bring cells into contact
D) hastens conjugation events
E) speeds up molecular movement of DNA

Question 15

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) The azi gene is closer to the thr and leu genes than the ton, lac, and gal genes.
B) The ton gene is found between the azi and lac genes.
C) Had the experiment continued, a time of entry map could be viewed for the entire E. coli chromosome.
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.

Question 16

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) The Hfr donor segment must undergo recombination in the recipient.
C) An F+ donor's T strand is slow to reach the pilus.
D) The Hfr donor transfers genes from the chromosome and not the plasmid.
E) The F+ donor segment must undergo recombination in the recipient.

Question 17

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

A) Generalized transduction uses lytic phage and specialized transduction uses a lysogenic phage.
B) Conjugation, transformation, and transduction all require recombination.
C) Conjugation requires cell- to- cell contact.
D) Conjugation, transformation, and transduction can all be used to map the order of genes on a bacterial chromosome.
E) Transformation requires a vector to carry donor DNA fragments to the recipient cell.

Question 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 $b \quad 0.04 \%$
$a$ and $c \quad 0.02 \%$
$b$ and $c \quad 0.0064 \%$ Which conclusion can be definitively made from this data?

A) Cotransformation of b and c is so frequent, they must be one gene.
B) Gene b is closer to c than to a.
C) Gene a is closer to c than to b.
D) Gene order is a, b, then c.
E) Genes b and c are farthest apart.

Question 19

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

A) Under the direction of phage genes, transcription and translation produce new phage components.
B) The phage DNA is injected into the host.
C) Progeny phage particles are released by lysis from host bacteria.
D) The phage DNA is integrated into the host chromosome.
E) The host DNA breaks down.

Question 20

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

A) F+ and Hfr cells cannot convert exconjugants to a donor state.
B) 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.
D) An F' cell can convert exconjugants to a donor state, as well as change their genotype.
E) An Hfr cell can convert exconjugants to a donor state, as well as change their genotype.

Question 21

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?

Question 22

Which of the following regarding lateral gene transfer is false?

A) It can convert benign bacteria into pathogens that cause disease.
B) It facilitates rapid genome evolution.
C) It may occur by conjugation, transformation, or transduction.
D) It increases the efficiency of antibiotics against normally sensitive strains.
E) It allows an organism to rapidly acquire whole segments of chromosomes containing multiple genes.

Question 23

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) Genes b and c are more closely linked than a and b or a and c.
B) The genes are all located extremely close to each other.
C) Genes b and c are found together only if double crossovers have occurred.
D) The gene order is a, b, c.
E) Genes a and b are more closely linked than a and c or b and c.

Question 24

What is the role of the relaxosome in conjugation?

Question 25

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

A) Intragenic recombination between mutants with partial deletions and point mutations could be used to map the position of individual rII mutations.
B) Deletion- mapping analysis found that a point mutation and a deletion mutation whose locations overlapped resulted in wild- type intragenic recombinants.
C) The size of the plaques on E. coli lawns determined the distance between rIIA and rIIB.
D) Intragenic recombination analysis could determine the distance between rIIA and rIIB.
E) Simultaneous infection of rII phage mutants resulted in T4 plaques when the mutations were in the same rII gene.

Question 26

A scientist is studying a gene (grn) carried by a bacteriophage that allows a host bacterium to produce a green metabolic product before lysis. The scientist has four bacteriophage mutants for this gene. Mutant 1 has a nonrevertible mutation in grn while Mutants 2, 3, and 4 each have a revertible mutation in grn. After plating pairs of mutants and subsequent coinfection of host cells, the scientist observed the following: I. Mutants 1 and 2: no green product
II) Mutants 1 and 3: very rare green product
III) Mutants 1 and 4: rare green product
Which of the following is NOT consistent with these observations?

A) Mutant 2 has a base- pair substitution at a different site than Mutant 3.
B) A green product should be observed if coinfection occurs with mutants 3 and 4.
C) Mutant 1's deletion is closer to the base- pair substitution in Mutant 3 than it is to the base- pair substitution in Mutant 4.
D) A partial deletion in Mutant 1 overlaps a base- pair substitution in Mutant 2.
E) Mutant 3 has a base- pair substitution at a different site than Mutant 4.

Question 27

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

Question 28

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

Question 29

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

Question 30

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 a different gene
B) the distance between the two types of mutation
C) that the point mutation is recessive
D) that the deletion includes the position of the point mutation in the same gene
E) that the point mutation is dominant

Question 31

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

Question 32

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) the first gene in the operon; complete media
B) a nearby essential metabolic gene downstream of the operon; complete media
C) a nearby essential metabolic gene upstream of the operon; complete media
D) a nearby essential metabolic gene upstream of the operon; minimal media supplemented with the corresponding essential metabolite
E) the first gene in the operon; minimal media supplemented with the corresponding essential metabolite

Question 33

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?

Question 34

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

Question 35

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⁺. $$\begin{array} { | c | c | } \hline \text { Transductant Genotyp } & \text { Number } \\\hline a + b - c + & 160 \\\hline a + b + c + & 360 \\\hline a + b + c - & 460 \\\hline a + b - c - & 20 \\\hline\end{array}$$ Which of the following conclusions is false?

A) The selected marker screen will inhibit growth of transductants with the genotype a^- b⁺ c^- .
B) The transduction frequency between a and b is 82%.
C) Gene a and gene b are closer together than gene a and gene c.
D) The gene order is acb.
E) The transduction frequency between a and c is 48%.

Question 36

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): $\begin{array}{ll}42 \text { and } 62 & + \\42 \text { and } 83 & - \\62 \text { and } 63 & - \\62 \text { and } 74 & + \\42 \text { and } 74 & \text { - } \\42 \text { and } 75 & + \\62 \text { and } 75 & \text { - }\end{array}$ What can you conclude?

A) Mutations 62 and 74 are in the same gene.
B) Mutation 63 is not in the same gene as either 62 or 42.
C) Mutations 62, 63, and 74 are in the same gene.
D) Mutations 42 and 75 are in the same gene.
E) Mutations 42 and 74 are in the same gene.

Question 37

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

A) An unselected marker screen identifies transductants for an additional donor allele of interest.
B) Selection identifies transductants that have acquired an even number of crossovers.
C) A selected marker screen identifies transductants for a donor allele of interest.
D) A low co- transduction frequency between two genes is evidence of linkage.
E) A high co- transduction frequency between two genes is evidence of linkage.

Question 38

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

Question 39

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?

Question 40

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

A) intragenic recombination analysis and deletion- mapping analysis only
B) genetic complementation analysis only
C) intragenic recombination analysis only
D) genetic complementation analysis, intragenic recombination analysis, and deletion- mapping analysis
E) deletion- mapping analysis only

Question 41

Conjugation, transduction, and transformation all occur in nature. Which do you expect would more likely account for the acquisition of the genes for resistance to an antibiotic? Why? Which do you think would best account for the acquisition of genes from one bacterial species by another of a different genus? Why?

Question 42

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

Question 43

What characterizes a bacterial cell that can undergo transformation?

Question 44

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

Question 45

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

Question 46

Bacteria that can grow on minimal medium are called
require one or more essential compounds for growth are called

Question 47

How are selective media used in studying bacterial recombination?

Question 48

An interrupted mating study is carried out on the Hfr strains 1, 2, and 3. A small sample of each mixture is collected every minute for 20 minutes after conjugation is established. Results for each of the three Hfr strains are shown below. The total duration of conjugation (in minutes) is given for each transferred gene.

Question 49

Which, if any, characteristics of bacterial gene transfer is/are useful in analyzing eukaryotic gene transfer?

Question 50

Explain when, why, and how recombination in bacteria is like crossing over in diploid cells.

Question 51

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

Question 52

Some bacteriophages can be either lytic or lysogenic. These are called _ phages.

Question 53

What distinguishes generalized versus specialized transduction?