topic_10_for_students(2) - Topic 10 Principles of Genetics...

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Unformatted text preview: Topic 10 Principles of Genetics II D N A t r a n s f e r Fig 1. transformation transfer of bacterial genes involving free DNA 2. transduction transfer of host genes from one host to another by a virus ig 3. conjugation transfer of genes from one prokaryotic cell to another by mechanism involving cell-to-cell contact and a plasmid R e c o m b i n a t i o n Genetic Recombination Recombination physical exchange of DNA between genetic elements Homologues genes or regions with significant sequence similarity Homologous recombination physical exchange of DNA between homologous sources Recombination SSB single-stranded binding protein RecA found in all prokaryotes, higher eukaryotes Resolution nucleases and ligase Fig Holliday Junctions Homologous DNA aligns Isomerization determines resolution http://tinyurl.com/hollidayjunction Selection Fig T r a n s f o r m a t i o n T r a n s d u c t i o n Transformation 1920s: Fredrick Griffith infected mice with Streptococcus pneumoniae Fig S: “smooth” colony morphology (encapsulated) R: “rough” colony morphology (no capsule) Transformation Observation of transformation set the stage for the discovery of DNA Cells capable of taking up DNA are competent Naturally competent cells regulate DNA uptake Cells can be made competent by treatment with salts (chemically competent cells) or by electricity (electrocompetent cells) Transformation Can transform linear DNA or plasmids Transformation events isolated by selection Plasmid transformation associated with antibiotic markers Fig Transduction Transfer of DNA between cells, mediated by bacteriophage Two modes of transfer, dependent on type of phage replication generalized transduction: random host DNA specialized transduction: site-specific host DNA Generalized Transduction Random packaging of host DNA Transduction event for a given gene is rare Fig Specialized...
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topic_10_for_students(2) - Topic 10 Principles of Genetics...

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