5. Genetics of Bacteria and Viruses

An Hfr strain is used to map three genes in an interrupted mating experiment. The cross is Hfr/a⁺b⁺c⁺ rif x F⁻/a⁻b⁻c⁻ rif^T (No map order is implied in the listing of the alleles; rif^T is resistance to the antibiotic rifampicin.) The a⁺ gene is required for the biosynthesis of nutrient A, the b⁺ gene for nutrient B, and the c⁺ gene for nutrient C. The minus alleles are auxotrophs for these nutrients. The cross is initiated at time = 0, and at various times, the mating mixture is plated on three types of medium. Each plate contains minimal medium (MM) plus rifampicin plus specific supplements that are indicated in the following table. (The results for each time interval are shown as the number of colonies growing on each plate.)

What is the purpose of rifampicin in the experiment?

Why are the recombinants produced from an Hfr x F⁻ cross rarely, if ever, F⁺?

True or False:For conjugation to occur, bacterial cells must physically contact each other.

What is the name of the structure through which DNA is transferred? 

What property does the F factor give bacteria?

A F⁺ bacterial cell can donate DNA to which type of bacterium?

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

Describe a "partial diploid" and how it originates.

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

Describe the results of conjugation (i.e., changes in the recipient and the exconjugant) that allow detection of the state of the F factor in a donor strain.

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

Which of these donors can transfer a donor gene to exconjugants?

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

Which of these donors can convert exconjugants to a donor state?