10.06.11 - Lecture 10. Recombination comes full circle...

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Lecture 10. Recombination comes full circle Reading: Chap 5, 173-195
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Concepts: 1.Recombination in prokaryotes and viruses occurs outside of the meiotic pathway and Mendel’s postulates 2.Nonetheless, recombination occurs in bacteria and viruses and allows genes to be mapped. 3.Bacterial recombination can occur through multiple mechanisms including conjugation ( sex), transformation , and transduction .
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An Hfr strain differs from an F+ strain in that: a). Hfr contains F factor DNA b). Hfr strains are unable to conjugate but F+ can. c). Hfr strains have the F factor in the chromosome d). Hfr strains can only mate with F+, whereas F+ can only mate with F-. Clicker question I
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pilus Conjugation occurs by the movement of DNA across a pilus
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Lederberg and Tatum’s experiment Strain A met bio + + Prototroph frequency Strain B + + thr leu Strain A + Strain B Plate on minimal media: only prototrophs grow
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Lederberg and Tatum’s experiment Why were prototrophs recovered? Why was Lederberg smart to use double mutants? How did they show this was due to a direct cell-cell contact? --++ The prototrophs were recovered through recombination Some form of recombination event appeared to be going on ++-- --++ --++ ++++ Reversion 1/10? Double reversion: need 2 independent mutations to occur 1/10^7 x 1/10^7 Used Davis tube
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F (fertility) factors Hayes and Cavalli-Sforza discovered “ donor ” (male) and “ recipient ” (female) strains donor strains have heritable F (fertility) factor (F + ): “male” = F + “female” = F - UNIDIRECTIONAL INHERITANCE – NOT SEX!!! Mating “cross” Progeny mating types F + x F - F+ all F - x F - F- all F + x F + F+ all fertile, rarely conjugate plasmid
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Plasmid ” - circular DNA carried and transmitted among bacteria cells. NOT part of the bacterial chromosome or “genome”. In matings with F+ cells, transfer of F factor (and mating type) happens MUCH more frequently than transfer of genomic material. In matings with F+ cells, transfer of F factor (and mating type) happens MUCH more frequently than transfer of genomic material. oriT - origin of conjugal transfer
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10.06.11 - Lecture 10. Recombination comes full circle...

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