1. Distinguish between each set of the following pairs:

1. F factor conjugation vs. HFr conjugation

2. Conversion vs. recombination in bacteria

3. F vs. F' factors

4. prototroph vs. auxotroph

5. F⁺ and Hfr

    

2. List and explain (briefly) three methods of determining map order and distance of genes in E. coli.  Which of these require Hfr strains?

3. An F⁺ strain of E. coli that is lac⁺ (A) gave rise to the three Hfr strains drawn below (B, C, and D) and one of these gave rise to a F'(lac⁺) strain (E). All five strains are mated individually to an F^-strain that is lac^-. (The arrow indicates the direction of replication.)

1. Rank the strains (highest to lowest) in terms of the frequency of conversion? Explain your ranking. 

2. Rank the strains in terms of the frequency of transfer of the lac⁺ gene? Again, explain your answer. 

3. Which Hfr strain gave rise to the F'(lac⁺) strain? Why (i.e. describe the derivation of F' strains)? 

4. Hfr strain C which is also met^-pro⁺ was mated to an F^- strain that is lac^-met⁺pro^-. Interrupted-mating studies show that the lac⁺ gene enters last, so lac⁺ exconjugates were picked and examined for the other two markers with the following results:

1. How would you select for lac⁺ exconjugates? 

2. Why are there no individuals of the lac⁺met^-pro^- genotype? 

3. What is the gene order? 

4. Which two genes are closest together on the genetic map? Give your reasoning and show how you would calculate the map distance (you do not have work out the calculation). 

4. A wild type Hfr strain is conjugated with an F^- strain that is a^-b^-c^-d^- and the following bacterial clones are selected because they are d⁺ (the d gene is the last to enter):

               a⁺b⁺c⁺               650

               a⁺b⁺c^-                  20

               a⁺b^-c⁺                  20

               a⁺b^-c^-                  30

               a^-b⁺c⁺                270

               a^-b⁺c^-                160

               a^-b^-c⁺                   0

               a^-b^-c^-                   50

1. What is the map order of the genes (d should be the LEFTMOST gene in your series).  Explain your answer.

2. Which two adjacent genes are closest together?  Explain. (You do not have to calculate map distances, but you may wish to add up crossover occurring between genes.)

3. Which two adjacent genes are furthest apart?  Explain.  (You do not have to calculate map distances but you may wish to add up crossover occurring between genes.)

4. Describe another way of determining the map order of these genes.

5. a. Seven deletion mutants of the bacteriophage T4 were crossed in paired combinations to test for their ability to produce wild-type recombinants. The results are given below, where + indicates that recombinants were formed. Construct a deletion map based on these data.
    

2. Five point mutations were tested in paired crosses with these deletions for their ability to yield recombinants. The results are given below. What is the relative order of the point mutations? 

6. P22, a generalized transducing phage, is grown on a pur⁺ pro⁺ his⁺ bacterial donor and then used to infect a recipient strain that is pur^- pro^- his^-. Later transductants for each donor gene are selected individually. In Experiment I pur⁺ transductants are selected, in Experiment II pro⁺ transductants are selected, and in Experiment III his⁺ transductants are selected.

1. What media are used for each selection experiment? 

2. The transductants are examined for the presence of unselected donor markers with the following results. What is the order of the bacterial genes? 

3. Without calculating map distance, how would you use the data above to estimate which genes are closest?  Which are these genes?

4. Which experiment is best to estimate relative distances between the three genes?  Explain.

5. Estimate the relative distance between the genes.

7. Distinguish between each set of the following pairs

1. Recombination vs. complementation at the rII locus of phage T4

2. lysis vs. lysogeny

3. General and specific transduction

8. Describe a genetic (not molecular) experiment to determine if mutations are in the same or different rII cistron.

Answers