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Microbial Genetics (Micr340)

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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  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. GeneralizedTransduction

  14. Co-Transduction

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