07-Bacteria - Bacteria and Bacteriophage Genetics genetic...

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Bacteria and Bacteriophage Genetics genetic recombination between bacterial strains conjugation F + and F - strains Hfr and F’ strains plasmids transformation bacteriophage life cycle transduction
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Serial dilutions and subsequent culture of bacteria on nutrient agar Prokaryotes have a single circular chromosome (~4M bp). smaller extrachromosomal plasmids may be present they reproduce by fission , dividing every 20 min. at 37 o C
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Genetic recombination between two auxotrophic strains Definitions : auxotroph : a mutant microorganism that requires a substance for growth that can be synthesized by wild type strains prototroph : a strain that can survive and grow on minimal growth medium (a wild type strain) Strain A : can synthesize threonine, leucine and thiamine, but not methionine or biotin Strain B : can synthesize methionine and biotin, but not threonine, leucine or thiamine neither auxotroph can grow in minimal medium ( lacking methionine, biotin, threonine, leucine and thiamine ), but when mixed together, recombination generates prototrophs (wild type cells that can synthesize all five) Lederberg & Tatum (1946)
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(1946) Genetic recombination between two auxotrophic strains
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Genetic recombination between two auxotrophic strains Recombination requires physical interaction between the two strains. The Davis experiment : placed the two auxotrophic strains in a U-tube, but separated them with a filter that allowed the common growth medium to pass between the chambers but did not allow cells through no recombination occurred : no prototrophs were recovered
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The Davis experiment Genetic recombination requires physical contact between cells.
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Conjugation Reproduction : the production of new individuals Sex : the combining of genes from two individuals to generate new genetic combinations Conjugation : the transfer of genetic information from one cell to another through a sex pilus (F pilus) Conjugation is unidirectional: always from a F + to a F - cell . F
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This note was uploaded on 11/13/2009 for the course PCB 3063 taught by Professor Sotero during the Fall '09 term at University of Central Florida.

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07-Bacteria - Bacteria and Bacteriophage Genetics genetic...

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