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Study Guide Test 5

Study Guide Test 5 - Chapter 5 Bacterial mutants are...

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Chapter 5 Bacterial mutants are detected by recombinants from the parents in the progeny. Rarely are two complete chromatids from the parents joined; instead, it is usually the union of one complete chromosome and a fragment of another. Gene Exchance o Conjugation: contact and fusion of two different cells Partial genome transfer Plasmid transfer o Transformation: take up a piece of DNA from external environment and incorporate into own chromosome. o Transduction: Phage picks up a piece of DNA from one bacterial cell and injects it into another, which can be incorporated into the chromosome. o Also, phage recombination: phages can undergo recombination when two different genotypes both infect the same bacterial cell Prototrophic: wild-type bacteria; can grow on minimal medium Auxotrophic: cells that will not grow unless medium contains particular cellular building blocks. No recombinants are produced without cell contact Fertility Factor: Only F+ can donate; replicates in the cytoplasm independent of the host chromosome o Rolling circle replication: Circular plasmid reels out single-stranded DNA, goes through pilus and replicates in host cell. Hfr strains create many more recombinants than F+ when crossed with F-. o In fact, the rare recombinants from F+ x F- were from spontaneous formation of Hfr cells. Interrupted Mating: Any antibiotic resistant cell bearing a donor allele must have taken part in conjugation and is called an exconjugant. o Each donor allele appears at a specific time after mating and in a specific sequence; later donor alleles are present in fewer cells because of breakage DNA transfer begins from a fixed point on the donor chromosome (origin) o This point is also known as the site where F plasmid is inserted o The farther a gene is from O, the later it is transferred to the F- Rareness of Hfr exconjugants is due to the fact that the inserted F is transmitted as the last element of the linear chromosome. o Thus, almost none of F- are converted If each strain is a segment of a circle, they can be mapped. o One end of integrated F factor is origin, where transfer of Hfr chromosome begins o The other end is the terminus In integrated F transformation, F is transmitted last; in plasmid state, F is only thing transferred, and is usually successful. Recombination takes place between a complete genome from F- (endogenote) and incomplete genome from Hfr (exogenote).
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o Partial diploid (merozygote): when the cell contains two copies of one segment of DNA (one part of endogenote, one part of exogenote) In order to keep viability and circular structure, an even number of crossovers must result (single crossover results in nonviable linear) For recombinant frequency analysis, we need trihybrid exconjugants o First, select stable exconjugants bearing the last donor allele (+); if you select for the last marker, then we know that such cells at some stage must have contained the earlier markers.
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Study Guide Test 5 - Chapter 5 Bacterial mutants are...

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