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

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Microbial Genetics (Micr340)

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Microbial Genetics (Micr340)

Lecture 10

Lytic Bacteriophages (II)


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


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


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


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


Recombination


Genetic Analysis of Phages

  • Complementation tests: the gene products synthesized from two different DNAs interact in the same cell to produce a phenotype.


Complementation


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”


A three factor cross to map rII genes


Deletional mapping


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.


GeneralizedTransduction


Co-Transduction


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