Microbial Recombination and Gene Transfer Questions and Answers

Q: Bacteria are capable of "sharing" genetic material that can be advantageous in certain environments. This type of gene transmission is an example of which of the following?

Correct answer: ConjugationConjugation is the sharing of genetic material through direct contact between bacterial cells, and it is the mechanism by which advantageous traits such as antibiotic resistance spread through a population. A conjugative plasmid encodes its own transfer machinery, so a single resistant cell can convert its neighbours - and, because plasmid host ranges are often broad, cells of other species too.The word "sharing" is the clue: the donor keeps a copy while passing one on. Transformation and transduction also move genes horizontally but depend on free DNA or a phage rather than on contact, and fission is ordinary cell division, which passes genes vertically to daughter cells.

Q: Which of the following term describes the relationship between a virus and host where no new viral particles are produced and the viral genome is replicated along with host chromosome?

Correct answer: LysogenyLysogeny is the relationship in which the viral genome is maintained and replicated along with the host chromosome while no new virions are produced. The integrated phage genome is called a prophage, and the bacterium carrying it is a lysogen, which passes it on to every daughter cell.The prophage represses its own lytic genes and can confer new properties on the host - diphtheria and cholera toxins are both prophage-encoded. Lysis is the opposite outcome, in which progeny virions are made and the cell bursts; transformation and conjugation are bacterial gene-transfer mechanisms, not host-virus relationships.

Q: Which of the following statement(s) is/are true in regards to F+ x F- mating events?

Correct answer: DNA is transferred from F+ to F- cellsIn an F+ × F− mating the DNA moves from donor to recipient - from F+ to F−. The F+ cell makes the sex pilus, contact is established, and one strand of the F plasmid is nicked at oriT and transferred; both cells then synthesise the complementary strand, so the recipient becomes F+.Transfer is therefore one-way, defined by which cell carries the F factor. The F− cell is not incapable of conjugating - it is a perfectly good recipient - it simply lacks the plasmid that encodes the machinery, so it cannot act as donor.

91.

Bacteria are capable of "sharing" genetic material that can be advantageous in certain environments. This type of gene transmission is an example of which of the following?

A.Transduction
B.Transformation
C.Fission
D.Conjugation

Answer: D

Correct answer: Conjugation

Conjugation is the sharing of genetic material through direct contact between bacterial cells, and it is the mechanism by which advantageous traits such as antibiotic resistance spread through a population. A conjugative plasmid encodes its own transfer machinery, so a single resistant cell can convert its neighbours - and, because plasmid host ranges are often broad, cells of other species too.

The word "sharing" is the clue: the donor keeps a copy while passing one on. Transformation and transduction also move genes horizontally but depend on free DNA or a phage rather than on contact, and fission is ordinary cell division, which passes genes vertically to daughter cells.

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92.

Which of the following term describes the relationship between a virus and host where no new viral particles are produced and the viral genome is replicated along with host chromosome?

A.Lysogeny
B.Lysis
C.Transformation
D.Conjugation

Answer: A

Correct answer: Lysogeny

Lysogeny is the relationship in which the viral genome is maintained and replicated along with the host chromosome while no new virions are produced. The integrated phage genome is called a prophage, and the bacterium carrying it is a lysogen, which passes it on to every daughter cell.

The prophage represses its own lytic genes and can confer new properties on the host - diphtheria and cholera toxins are both prophage-encoded. Lysis is the opposite outcome, in which progeny virions are made and the cell bursts; transformation and conjugation are bacterial gene-transfer mechanisms, not host-virus relationships.

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93.

Which of the following statement(s) is/are true in regards to F+ x F- mating events?

A.DNA is transferred from F- to F+ cells
B.DNA is transferred from F+ to F- cells
C.No DNA is transferred because F- cells are unable to perform conjugation
D.No DNA is transferred because F+ cells are unable to perform conjugation

Answer: B

Correct answer: DNA is transferred from F+ to F- cells

In an F⁺ × F⁻ mating the DNA moves from donor to recipient - from F⁺ to F⁻. The F⁺ cell makes the sex pilus, contact is established, and one strand of the F plasmid is nicked at oriT and transferred; both cells then synthesise the complementary strand, so the recipient becomes F⁺.

Transfer is therefore one-way, defined by which cell carries the F factor. The F⁻ cell is not incapable of conjugating - it is a perfectly good recipient - it simply lacks the plasmid that encodes the machinery, so it cannot act as donor.

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94.

In specialised transduction, the genes transferred are

A.only those adjacent to the prophage integration site
B.any genes of the host chromosome
C.only plasmid genes
D.only phage genes

Answer: B

Correct answer: only those adjacent to the prophage integration site

In specialised transduction only the host genes adjacent to the prophage integration site can be transferred. The mechanism explains the restriction. A temperate phage integrates at a specific site, and when it excises it occasionally does so imprecisely - cutting a little to one side, so that it leaves some phage DNA behind and carries an equivalent length of neighbouring host DNA away. Only genes physically next to the integration site can be picked up this way. The classic example is phage lambda in E. coli, which integrates between the gal and bio genes and can therefore transduce only those. The contrast with generalised transduction is the point examined. There the phage packages a random fragment of fragmented host DNA during the lytic cycle, so any gene may be carried with roughly equal probability. The resulting particles are usually defective, having exchanged phage genes for host ones.

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