Lecture 19

Question 1

What is a plaque?

Answer 1

Something that forms after a bacterial colony is infected by bacteriophage resulting in lysis of the cells causing a plaque

Question 2

How can plaque morphology be used as an indicator of genotype?

Answer 2

It can be used to examine the characteristics of rapid lysis mutants and host range mutants

Question 3

How can phage crosses be done?

Answer 3

A mixed/double infection of the bacteria is done at a high multiplicity of infection, the progeny of these phage can then have their genotype identified in terms of rapid lysis and host range through plating with specific bacteria allowing recombinants to be determined and recombination frequencies to be calculated

Question 4

What are the two kinds of transduction?

Answer 4

Generalized transduction where any part of the host chromosome is mobilized
Specialised transduction where only specific, restricted regions of the chromosome are mobilized

Question 5

How are linkages expressed in transduction experiments?

Answer 5

Cotransductions frequencies, where a greater cotransduction frequency means the genetic markers are closer

Question 6

How are stable specialised transduction phages generated?

Answer 6

Outlooping of a prophage can remove part of the flanking bacterial DNA, these phages are defective but will infect a cell and integrate its genome if helper functions are provided through a wild type phage. These infected cells are unstable but if there is a double crossover with a defective phage genome then it will stabilize.