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lecture 11 - Gene Transfer Mutation and Genome Evolution...

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Unformatted text preview: Gene Transfer, Mutation and Genome Evolution The Mosaic Nature of Genomes • Microbial genomes have undergone extensive gene loss and gain • DNA sequence is not static – Mutations of single bases – slow, but accumulated through time – Large deletions – Large insertions of sequence – genetic islands • Transferred from other species – horizontal gene transfer • Introduce new functions • Maintained if confer growth advantage in specific environmental conditions – natural selection – Plasmids Horizontal Gene Transfer • Horizontal or lateral gene transfer : genes transferred from one organism to another ( donor to recipient ) – As opposed to vertical gene transfer: from mother cell to daughter cells through cell division • Three transfer processes: – Transformation : • Natural transformation: free (naked) DNA taken up from the environment and then integrated into genome • Plasmid transformation – Conjugation : cell-cell contact (sex pilus) – Transduction : DNA transfer is mediated by bacteriophage Discovery of Transformation • First demonstrated with Streptococcus pneumoniae by Griffith (1928); Avery and McLeod (1943): – mortality experiment with mice using smooth (with capsule, virulent) and rough (no capsule, nonvirulent) strain – Tested polysaccharide, protein, RNA, and DNA, and only DNA from smooth strain conferred virulence to rough strain Gene Transfer: Transformation...
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lecture 11 - Gene Transfer Mutation and Genome Evolution...

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