5. Genetics of Bacteria and Viruses

For bacteria that are F⁺, Hfr, F', and F⁻ perform or answer the following.Describe the state of the F factor.

In this chapter, we have focused on genetic systems present in bacteria and on the viruses that use bacteria as hosts (bacteriophages). In particular, we discussed mechanisms by which bacteria and their phages undergo genetic recombination, which allows geneticists to map bacterial and bacteriophage chromosomes. In the process, we found many opportunities to consider how this information was acquired. From the explanations given in the chapter, what answers would you propose to the following questions?How do we know whether or not genetic recombination between bacteria involves cell-to-cell contact?

The flow diagram identifies relationships between bacterial strains in various F factor states. For each of the four arrows in the diagram, provide a description of the events involved in the transition.

Conjugation between an Hfr cell and an F⁻ cell does not usually result in conversion of exconjugants to the donor state. Occasionally, however, the result of this conjugation is two Hfr cells. Explain how this occurs.

With respect to F⁺ and F⁻ bacterial matings, answer the following questions:What is the genetic basis for a bacterium's being F⁺.

With respect to F⁺ and F⁻ bacterial matings, answer the following questions:How was it established that chromosome transfer was unidirectional?

With respect to F⁺ and F⁻ bacterial matings, answer the following questions:How was it established that physical contact between cells was necessary?

Bacteria transfer genes by conjugation, transduction, and transformation. Compare and contrast these mechanisms. In your answer, identify which if any processes involve homologous recombination and which if any do not.

List all major differences between (a) the F⁺ x F⁻ and the Hfr x F⁻ bacterial crosses; and (b) the F⁺, F⁻, Hfr, and F' bacteria.

Explain the importance of the following features in conjugating donor bacteria:the origin of transfer