1. Microbial Genetics (Micr340) Lecture 10 Lytic Bacteriophages (II)

2. Genetic Analysis of Phages Genetic analysis – study of relationship (and distance) between different mutants using genetic approaches such as recombination and complementation Phage’s advantages: Short generation time Haploid Phages multiply as clones in plaques Different phages can be crossed

3. Genetic Analysis of Phages Infection of cells by phages: Permissive host Nonpermissive host Permissive conditions Nonpermissive conditions Multiplicity of Infection (MOI) – the efficiency of infection is affected not only by the concentration of phage and bacteria but also by the ratio of phage to bacteria

4. Genetic Analysis of Phages Phage crosses – the process in which the mutated DNAs of two members of the same species are put together in the same cell to allow recombination

5. Genetic Analysis of Phages Recombination tests – the DNA of two parent organisms is assembled in new combinations, so that the progeny have DNA sequences from both parents Recombination frequency: the closer the two regions of sequence difference are to each other, the less room there is for a cross over to occur

6. Recombination

7. Genetic Analysis of Phages Complementation tests: the gene products synthesized from two different DNAs interact in the same cell to produce a phenotype.

8. Complementation

9. Genetic Analysis of T4 phage Experiments with rII genes r-type of mutations for T4 phage – cause the infected cells to lyse more quickly than the normal (r+) phage rII = “rapidly-lysis mutants type II”

10. A three factor cross to map rII genes

11. Deletional mapping

12. Generalized Transduction Transduction – a process in which bacteriophages carry bacterial DNA from one cell to another during it infect-and-kill cycles Generalized transduction – any region of the bacterial chromosome can be transferred Specialized transduction – only certain genes close to the attachment site of a lysogenic phage in the chromosome can be transferred.

13. Generalized Transduction

15. Co-Transduction