Question 1

Bacterial gene transfer is also used in the lab to introduce genes into organisms of different species, genera, phyla, or even kingdoms or domains. A major example is the use of a Ti plasmid of the soil bacterium Agrobacterium tumefaciens to transfer genes into dicotyledonous plants. The bacterium infects the plant root in the soil and transfers some of the Ti plasmid genes (T DNA)into the plant nucleus. Recombination may occur, and T DNA expression is controlled by plant compounds generated in response to wounding and infection. The T DNA is generated when there is a nick that creates a primer for replication, followed by transfer of a single-stranded DNA piece that converts to a double-stranded piece in the plant nucleus. Which of these processes is Ti plasmid transfer most like?
A)conjugation
B)generalized transduction
C)specialized transduction
D)transformation

Accepted Answer

The Ti plasmid transfer is most like conjugation because it involves direct transfer of DNA from one organism (bacterium) to another (plant) through a physical connection, similar to how DNA is transferred between bacteria during conjugation.

Question 2

A bacterial cell containing an F factor is a threonine prototroph. Conjugation occurs with an F^- threonine auxotrophic cell. The exconjugant cell can grow on medium lacking threonine. Where was the F factor in the donor cell? A)F plasmid B)Hfr chromosome C)R plasmid D)A or B are both possible. E)A, B, or C are all possible.

Accepted Answer

C

Question 3

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

Accepted Answer

C

Question 4

In an imagined transduction experiment with alleles a⁺, b⁺, and c⁺, a⁺ alone was transduced into an auxotroph 1400 times, b⁺ alone 1200 times, and c⁺ alone 970 times. Genes a⁺ and b⁺ were both found 10 times, b⁺ and c⁺ 2 times, and a⁺ and c⁺ one time. What can you conclude? A)Cotransduction is too infrequent to be used to map genes. B)Genes a and c cotransduce only accidentally. C)Genes a and b are more closely linked than a and c or b and c. D)Genes a and c are found together only if double crossovers have occurred. E)Transduction of gene c is very rare.

Accepted Answer

Genes a and b were found together more frequently (10 times) than a and c (1 time), or b and c (2 times). This suggests that genes a and b are more closely linked and are more likely to be cotransduced than a and c or b and c.

Question 5

To integrate an F plasmid's genes into a host chromosome, there must be DNA recombination at homologous regions on the two circular strands. What is the minimum number of such crossover events needed for integration?
A)1
B)2
C)3
D)4
E)8

Accepted Answer

One crossover event is sufficient for integration, as it can result in the formation of a cointegrate structure, in which the F plasmid and the host chromosome are linked together.

Question 6

Bacterial gene transfer is also used in the lab to introduce genes into organisms of different species, genera, phyla, or even kingdoms or domains. A major example is the use of a Ti plasmid of the soil bacterium Agrobacterium tumefaciens to transfer genes into dicotyledonous plants. The bacterium infects the plant root in the soil and transfers some of the Ti plasmid genes (T DNA)into the plant nucleus. Recombination may occur, and T DNA expression is controlled by plant compounds generated in response to wounding and infection. This method can be used to introduce a gene for an antigenic protein into an edible plant, such as a potato, to produce an edible vaccine (e.g., for cholera). What has to be made a part of the Ti plasmid?
A)a gene for cholera resistance
B)a gene for a subunit of cholera toxin, including its regulatory elements
C)a gene for that part of the human immune system that neutralizes cholera
D)a molecule of anti-cholera antibody
E)a polypeptide that can attach the T DNA to plant DNA

Accepted Answer

A gene for a subunit of cholera toxin, including its regulatory elements, is required to produce an edible vaccine for cholera. This gene can be inserted into the Ti plasmid of Agrobacterium tumefaciens and transferred into an edible plant, which will then produce the antigenic protein that will act as a vaccine against cholera.

Question 7

Bacterial gene transfer is also used in the lab to introduce genes into organisms of different species, genera, phyla, or even kingdoms or domains. A major example is the use of a Ti plasmid of the soil bacterium Agrobacterium tumefaciens to transfer genes into dicotyledonous plants. The bacterium infects the plant root in the soil and transfers some of the Ti plasmid genes (T DNA)into the plant nucleus. Recombination may occur, and T DNA expression is controlled by plant compounds generated in response to wounding and infection. Assuming you have appropriately engineered the Ti plasmid to carry the gene in question, how could you best and most safely test whether your potatoes are now working as a vaccine?
A)Feed the engineered potato to a population at high risk for cholera.
B)Cook the potatoes to denature the toxin and feed them to mice susceptible to cholera.
C)Feed pieces of raw potato to susceptible mice and test them for antibodies.
D)Emulsify the potatoes in a liquid that can be injected into experimental animals.

Accepted Answer

The safest and most ethical approach would be to feed pieces of raw potato to susceptible mice and test them for antibodies. This would not involve any harm to humans or animals and would allow for the detection of an immune response, indicating that the vaccine is working. Option A is not ethical as it involves feeding an unproven vaccine to a population at high risk without prior animal testing. Option B is not ideal as cooking the potatoes could denature the protein and affect its efficacy as a vaccine. Option D involves injection, which could be more invasive and potentially risky than feeding.

Question 8

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⁺str^R and F^- cells of genotype a^-b^-c^-d^-e^-str^S 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. This graph shows the results of plating the cultures of 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

Accepted Answer

The order of the genes can be determined by analyzing the pattern of the transfer of markers at different time points. The first transferred gene should be the one closest to the origin of transfer. From the graph, it is clear that gene a is transferred first, followed by c, then e, then b, and finally d (which is not transferred in the experiment). Therefore, the correct order is a-c-e-b-d, which corresponds to choice B.

Question 9

In phi X 174 phage, whose genome is a single-stranded, circular DNA known as the - strand, replication occurs by the rolling circle method. In which order must the events of replication occur?
A)nicking of the - strand, binding of relaxase protein to the 5′ end, DNA synthesis of a + strand, separation of + from - strands, circularization of both strands
B)synthesis of a + strand, nicking at the origin, binding of protein to the 5′ end, DNA synthesis, displacement of the + strand when replication passes the origin, circularization of the + strand
C)synthesis of a + strand, nicking of both strands to separate them, recircularization of both strands
D)binding of a protein at the origin of the - strand, synthesis of a + strand, release of the + strand

Accepted Answer

The rolling circle method of replication in phi X 174 phage involves the synthesis of a complementary + strand, followed by nicking at the origin and displacement of the original - strand as replication proceeds. The newly synthesized + strand is then circularized to form the final double-stranded DNA molecule. Binding of a protein to the 5′ end is not necessary for replication in this system.

Question 10

In a partially diploid F′ exconjugant, there are two alleles for lac (1 and 2)and two alleles for his (3 and 4). The phenotype of this cell is identical to a lac 1 his 4 cell. What is the best interpretation?
A)Lac 1 and 2 and his 3 and 4 share only lac 1 and his 4 phenotypes.
B)Lac 1 complements lac 2 and his 3 complements his 4.
C)Lac 1 and his 4 are dominant.
D)Lac 1 and his 4 are wild types.
E)Lac 1 shows its phenotype only if his 4 is also present.

Accepted Answer

Lac 1 and his 4 are dominant because the phenotype of the cell matches that of a lac 1 his 4 cell, indicating that these alleles determine the phenotype.

Question 11

A large region of the F plasmid (~33 kb)is called the transfer region (tra)and contains about 40 genes necessary for conjugation. The gene traA codes for the protein pilin that is polymerized To form a pilus, using a number of other tra genes. The pilus is a hollow cylinder whose units disassemble once contact is made in order to "reel in" the recipient cell. What other functions of The tra genes are required for transfer? A)DNA unwinding, and prevention of contact with F⁺ cells B)enzymatic DNA replication C)resistance to phage infection D)integration of F genes into the recipient's chromosome E)integration of F genes into the recipient's plasmid

Accepted Answer

The tra genes are necessary for conjugation, the process of transferring genetic material from one bacterial cell to another. In addition to the gene for pilin, the transfer region includes genes that encode for proteins involved in DNA unwinding and preventing contact with incompatible cells. Therefore, option A is the best choice as it describes two functions of tra genes that are required for transfer - DNA unwinding and prevention of contact with incompatible cells. Enzymatic DNA replication, resistance to phage infection, and integration of F genes are not functions of the tra genes required for transfer.

Question 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⁺str^R and F^- cells of genotype a^-b^-c^-d^-e^-str^S 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

Accepted Answer

The answer of To map genes of a bacterial strain,...

Question 13

A competent Hemophilus strain is individually transformed by three genes (a, b, and c)at a rate of 0.002% each. However, cotransformation frequencies for each pair are as follows: a and b 0.38 %
A and c 0.72%
B and c 0.19%
What is the correct conclusion from this data?
A)Genes b and c are farthest apart.
B)Gene order is c, b, a.
C)Cotransformation of b and c is so frequent, they must be one gene.
D)Gene a is closer to b than to c.
E)Genes a and c are farthest apart.

Accepted Answer

The answer of A competent Hemophilus strain is individually transformed...

Question 14

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

Accepted Answer

The answer of In generalized transduction, a phage introduces a...

Question 15

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

Accepted Answer

Each strain entered the recipient cells in a specific order, as shown by the letters indicating the genes. To compile a correct time-of-entry map, we need to combine these orders in a way that makes sense. Starting with strain 1, we see that it enters as S L A C T F. Strain 2 enters as N P F T C A, but we notice that it shares the gene order F T C with strain 1. Similarly, strain 3 enters as T F P N U Y, sharing the genes F and N with strains 1 and 2. Strain 4 enters as S H Y U N P, sharing genes S and N with strains 1 and 2, and strain 5 as U N P F T C, which shares the genes N, P, F, and T with the previous strains.

By combining these orders, we can build a time-of-entry map that includes all the genes. The correct order for the genes is: S L A C T F P N U Y H. This order starts with the genes from strain 1, then adds the unique genes from each subsequent strain. The correct choice is therefore E.

Question 16

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

Accepted Answer

The answer of Which of the following allows the compilation...

Question 17

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 -
Mutation 42 has previously been shown to be in a different gene than mutation 62. 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.

Accepted Answer

Mutations 42 and 74 complement each other (+), indicating that they are in different genes. Mutations 62 and 74 also complement each other (+), indicating that they are in the same gene. Similarly, mutations 42 and 75 complement each other (+), indicating that they are in the same gene. Mutations 62 and 63 do not complement each other (-), indicating that they are in the same gene as each other but in a different gene from mutations 42 and 74. Therefore, the correct conclusion is that mutations 42 and 74 are in the same gene, while mutations 62, 63, and 74 are in a different gene from mutation 42.

Question 18

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.

Accepted Answer

Hfr donors integrate the F factor into their chromosome, allowing them to transfer chromosomal genes at a higher rate during conjugation.

Question 19

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

Accepted Answer

In order for stable integration to occur, the recipient cell must circularize the transferred single-stranded DNA. Additionally, replication of the new recipient DNA is necessary for stable maintenance of the transferred DNA. Stopping the rolling circle replication after one copy length ensures that only one copy of the F plasmid DNA is transferred.

Question 20

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+str^R and F^- cells of genotype a^-b-c-d-e-str^S 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

Accepted Answer

The answer of To map genes of a bacterial strain,...

Quiz 6: Genetic Analysis and Mapping in Bacteria and Bacteriophages

A bacterial cell containing an F factor is a threonine prototroph. Conjugation occurs with an F^- threonine auxotrophic cell. The exconjugant cell can grow on medium lacking threonine. Where was the F factor in the donor cell?

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?

In an imagined transduction experiment with alleles a⁺, b⁺, and c⁺, a⁺ alone was transduced into an auxotroph 1400 times, b⁺ alone 1200 times, and c⁺ alone 970 times. Genes a⁺ and b⁺ were both found 10 times, b⁺ and c⁺ 2 times, and a⁺ and c⁺ one time. What can you conclude?

To integrate an F plasmid's genes into a host chromosome, there must be DNA recombination at homologous regions on the two circular strands. What is the minimum number of such crossover events needed for integration?

In phi X 174 phage, whose genome is a single-stranded, circular DNA known as the - strand, replication occurs by the rolling circle method. In which order must the events of replication occur?

In a partially diploid F′ exconjugant, there are two alleles for lac (1 and 2) and two alleles for his (3 and 4) . The phenotype of this cell is identical to a lac 1 his 4 cell. What is the best interpretation?

A competent Hemophilus strain is individually transformed by three genes (a, b, and c) at a rate of 0.002% each. However, cotransformation frequencies for each pair are as follows: a and b 0.38 % A and c 0.72% B and c 0.19% What is the correct conclusion from this data?

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?

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

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

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