Question 1

Which of the following statements best explains why traditional Mendelian genetic crosses are not used in bacterial genetics?

Accepted Answer

Bacteria reproduce asexually by binary fission, so allelic differences exist between strains, not within a single organism.

Question 2

In the Lederberg and Tatum experiment, why did colonies only appear on minimal medium plates when two different auxotrophic E. coli strains were mixed together?

Accepted Answer

Genetic material was transferred between the strains, producing prototrophic recombinants able to synthesize all required nutrients.

Question 3

Which experimental result from the Davis U-tube experiment provided evidence that conjugation requires direct physical contact between bacterial cells?

Accepted Answer

No prototrophic colonies appeared when the two strains were separated by a filter that allowed DNA but not cells to pass.

Question 4

Which of the following best describes the role of the F factor in E. coli conjugation?

Accepted Answer

It is a plasmid that carries genes required for the formation of sex pili and DNA transfer.

Question 5

During conjugation between an Hfr cell and an F-minus cell, why does the recipient cell typically remain F-minus after the process?

Accepted Answer

The entire Hfr chromosome, including the F factor, rarely transfers because conjugation is usually interrupted before transfer is complete.

Question 6

In an interrupted conjugation experiment, the order of gene transfer from an Hfr donor to an F-minus recipient is thr, leu, azi, ton, lac, gal. If the lac gene begins to appear in recipient cells at 16 minutes and the gal gene at 25 minutes, what is the approximate map distance between lac and gal?

Accepted Answer

$$9$$ minutes

Question 7

Which of the following best describes the process of bacterial transformation?

Accepted Answer

A bacterium takes up extracellular DNA from the environment and incorporates it into its chromosome by recombination.

Question 8

A laboratory technician wants to introduce a plasmid carrying an antibiotic resistance gene into E. coli. Which artificial transformation method could be used to increase the permeability of the bacterial cell membrane to DNA?

Accepted Answer

Treating cells with calcium chloride followed by heat shock.

Question 9

Which of the following is NOT a category of plasmid described in the study materials?

Accepted Answer

Replication origin plasmids

Question 10

A bacterium is described as 'competent.' What does this mean in the context of genetic transfer?

Accepted Answer

It is able to take up extracellular DNA from the environment.

Question 11

Which of the following scenarios is an example of horizontal gene transfer?

Accepted Answer

A bacterium acquires a gene for antibiotic resistance from a plasmid transferred by conjugation.

Question 12

Which mechanism of genetic transfer is most likely responsible for the rapid spread of methicillin resistance among Staphylococcus aureus strains, as seen in MRSA?

Accepted Answer

Horizontal gene transfer, such as conjugation or transformation

Question 13

A bacteriophage accidentally packages a fragment of host DNA containing the his-plus gene and transfers it to a his-minus recipient cell. What is this process called?

Accepted Answer

Transduction

Question 14

Which of the following best describes the difference between homologous and non-homologous recombination during transformation?

Accepted Answer

Homologous recombination requires sequence similarity between incoming DNA and the chromosome, while non-homologous recombination does not.

Question 15

If a bacterial cell acquires a plasmid carrying genes for antibiotic resistance, which category of plasmid is most likely involved?

Accepted Answer

Resistance plasmid (R factor)

Question 16

Which of the following steps occurs LAST during the process of F factor transfer from an F-plus to an F-minus cell?

Accepted Answer

Relaxase joins the ends of the single-stranded DNA to form a circular molecule in the recipient cell.

Question 17

A researcher isolates a strain of E. coli that can transfer chromosomal genes at a high frequency during conjugation. Which genetic event most likely produced this strain?

Accepted Answer

Integration of the F factor into the bacterial chromosome, creating an Hfr cell.

Question 18

Which of the following best explains why the E. coli genetic map is described as '100 minutes long'?

Accepted Answer

It takes approximately 100 minutes to transfer the entire chromosome during an Hfr mating.

Question 19

Which of the following is a real-world consequence of horizontal gene transfer among bacteria?

Accepted Answer

The emergence and spread of multidrug-resistant pathogens in hospitals.

Genetic Transfer and Mapping in Bacteria (Chapter 7 Study Notes)

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