ZOL341_SS07_Lecture05

ZOL341_SS07_Lecture05 - Last Class Bacterial Genetics...

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Unformatted text preview: Last Class Bacterial Genetics Transformation Conjugation Hfr E. coli The sex factor of E. coli (F-plasmid) can recombine into the circular bacterial chromosome The fusion creates a high frequency recombination (Hfr) strain. Hfr conjugation and DNA transfer F` Plasmids Abnormal excision of the F-factor from the Hfr chromosome can transfer chromosomal genes to the excised F-plasmid (now named F`-factor; F`(lac) in the example shown) Used to create partial diploids (merodiploids) to test genetics of a specific gene First evidence of mobile elements Joshua Lederberg and Edward Tatum Auxotrophic E. coli Unable to synthesize a necessary compound or amino acid for growth Will grow if that compound or a.a. is provided within the media Y10 (thr- , leu- , thi- ) Y24 (bio- , phe- , cys- ) Followed by Bernard Daviss Experiment Direction Transfer Random integration Hfr and mapping Map the order of elements on a piece of DNA Time of entry mapping The time of entry of genes into the F- cells can be used to make genetic maps Different Hfr strains transfer genes starting at different locations and in one of 2 different orientations (clockwise or counter-clockwise). The relative location of the genes (genetic map) remains the same Genetic Map of E. coli E. coli map s howing some of the about 4,000 total genes Note that the map is in minutes rather than in map units. It takes 100 minutes to transfer the entire E. coli chromosome to a F- cell. Closer view of Genetic Map Details of 2 minutes (2%) of the E. coli genetic map The single origin of DNA replication (oriC) in the chromosome is located at about 84.4 minutes. Viral Genetics Temperate Phage P1 Phage and Transduction When a bacteriophage can transfer any bacterial gene, the process is called generalized transduction Transduction mapping Transduction can be used for mapping genes at a higher resolution than is possible by conjugation mapping Lytic Cycle of Phage Infection of a bacterial lawn by a lytic bacteriophage creates a clear spot (plaque) due to the lysis of bacteria Phage Genetic Map Results of a number of phage crosses can be combined to generate the complete genetic map of a bacteriophage chromosome Genetic Map of T4 Phage Bacteriophage T4 chromosome is approximately 167,000 base pairs in size. The chromosome is linear but the genetic map is circular Terminal redundency of T4 Bacteriophage T4 chromosome is circularly permuted and terminally redundant Benzers mapping of rII Deletion Mapping...
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ZOL341_SS07_Lecture05 - Last Class Bacterial Genetics...

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