Transcript 8-Genetics
Bacterial Genetics (Chapter 7) The beginning of Chapters 7 is largely a review of topics covered in Biol 131, and our focus will be on the sections beginning with “Mutations to Genes” We will discuss the basic steps used in genetic engineering, and you should read the pertinent sections of Chapter 8. How is knowledge of bacterial mutation and recombination important? -- Evolution -- Antibiotic resistance -- Genetic engineering How do bacteria obtain new traits? Spontaneous mutation -- or experimentally ‘induced’ From other cells “Genetic recombination” Bacterial Genetics 1 The Bacterial Chromosome Basic structure DNA double helix no nucleosomes Replication Plasmids DNA replication Bacterial Genetics 2 Genetic mutations are changes to the genetic code Some common types and effects of mutations chemical alterations base substitution deletions -- cause shift in ‘reading frame’ Bacterial Genetics 3 What are the causes of mutations? “Spontaneous” vs Induced “Mutagens” Chemicals UV light Ionizing radiation Bacterial Genetics 4 Mutations and evolution of bacteria Do all mutations lead to beneficial changes? Do mutations create beneficial changes in response to specific environment ‘stresses’ (such as high temperature)? Will a beneficial mutation always spread through a population? -- under what conditions? Bacterial Genetics 5 The Ames test -- book doesn’t describe this well Bioassay for chemical mutagenicity Salmonella typhimurium used is a His- ‘auxotroph’ “Positive selection” for a ‘back mutation’ to His+ (compare to negative selection in the book) mutagens and carcinogens Bacterial Genetics 6 Bacterial Genetic Recombination Processes by which bacterial genes are obtained from other organisms = “Horizontal gene transfer” Three processes: 1) Transformation 2) Conjugation 3) Transduction Bacterial Genetics 7 Transformation Griffith & Avery Studies Gene sources ‘Competent’ cells Transformation Bacterial Genetics 8 Transduction Transfer mediated By virus In “Specialized transduction” Specific genes are passed Transduction Bacterial Genetics 9 Conjugation Genes carried on a F-plasmid Process of conjugation Loss of F+ phenotype Plasmids can carry other genes R-plasmids Conjugation Virulence plasmids Other nonessential traits Bacterial Genetics 10 Hfr mediated conjugation ‘High frequency of recombination’ Plasmid integration Consequences Bacterial Genetics 11 Use of Bacteria in Biotechnology Role of plasmids ‘Cloning’ of useful genes Bacterial ‘drug factories’ Bio-engineering of other organisms Genetic Engineering Bacterial Genetics 12