Exam 6: Genetic Analysis and Mapping in Bacteria and Bacteriophages

A large region of the F plasmid (~33 kb)is called the transfer region (tra)and contains about 40 genes necessary for conjugation. The gene traA codes for the protein pilin that is polymerized To form a pilus, using a number of other tra genes. The pilus is a hollow cylinder whose units disassemble once contact is made in order to "reel in" the recipient cell. What other functions of The tra genes are required for transfer?

In an imagined transduction experiment with alleles a⁺, b⁺, and c⁺, a⁺ alone was transduced into an auxotroph 1400 times, b⁺ alone 1200 times, and c⁺ alone 970 times. Genes a⁺ and b⁺ were both found 10 times, b⁺ and c⁺ 2 times, and a⁺ and c⁺ one time. What can you conclude?

Once a phage genome has become part of the host chromosome, it is called a ________.

If you count 73 plaques on a bacterial plate after you had plated 0.1 ml of a 10^-4 dilution of phage, what was the initial concentration of the (undiluted)phage?

Prototrophs are bacteria that can grow on ________ medium.

A bacterial cell containing an F factor is a threonine prototroph. Conjugation occurs with an F^- threonine auxotrophic cell. The exconjugant cell can grow on medium lacking threonine. Where was the F factor in the donor cell?

To map genes of a bacterial strain, conjugation must be interrupted at given times. Suppose you have Hfr cells of genotype a⁺b⁺c⁺d⁺e⁺str^R and F^- cells of genotype a^-b^-c^-d^-e^-str^S and you combine these two cultures in liquid medium in four blenders at time 0. After intervals of 3, 6, 9, and 12 minutes, you turn on successive blenders. This graph shows the results of plating the cultures of each blender. What is the correct order of the genes on this chromosome?

Which form of bacterial recombination requires no vector?

If conjugation occurs with an F′ donor, how will the recipient be characterized genetically?

In a transduction experiment, what would constitute evidence of linkage?

Arabinose sugar is used by ara⁺ bacteria but cannot be used by ara^- mutants. When both ara3 and ara5 mutants are introduced into the same recipient via a vector, and the recipients still cannot use arabinose, what can you conclude?

What is the difference between F⁺ and F^- bacteria?

Name the three usual phases of bacterial growth in a liquid medium.

In conjugation, as the 5′ end of the T strand begins to move across the pilus, what form of replication occurs in the donor cell?

What is the role of the relaxosome in conjugation?

In his analysis of rII in phage, Benzer assayed complementation. Suppose you try your hand at this with several mutants and get the following results (+ = complementation): 42 and 62 + 42 and 83 - 62 and 63 - 62 and 74 + 42 and 74 - 42 and 75 + 62 and 75 - Mutation 42 has previously been shown to be in a different gene than mutation 62. What can you conclude?

Describe two features of a plasmid.

All three types of bacterial recombination share one characteristic. What is it?

What distinguishes generalized versus specialized transduction?

One kind of plasmid in bacteria is called an R plasmid. What kinds of genes are typical of such plasmids?