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Chapter 8: Bacterial Genetics

Chapter 8: Bacterial Genetics. Genetic changes in bacteria occur via: -mutations -gene transfer. What are mutations?. Change in the base sequence of the DNA Do they always change the genetic code?. Causes of mutations in bacteria. Most are spontaneous Errors made by DNA Polymerase

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Chapter 8: Bacterial Genetics

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  1. Chapter 8: Bacterial Genetics

  2. Genetic changes in bacteria occur via: -mutations -gene transfer

  3. What are mutations? Change in the base sequence of the DNA Do they always change the genetic code?

  4. Causes of mutations in bacteria Most are spontaneous Errors made by DNA Polymerase UV light exposure

  5. Types of Mutations Base-pair mutation Missense mutation Nonsense mutation Silent mutation

  6. Base-pair mutation: missense

  7. Results of base-pair mutations

  8. Types of Mutations • Frameshift • Changes the reading frame

  9. What can cause mutations? Chemicals (nitrous acid) Physical mutagens (uv light) Biological mutagens (transposons)

  10. Barbara McClintock: “jumping genes” biological mutagen

  11. Nitrous acid as a chemical mutagen

  12. Nitrosoguanidine alters guanine bases

  13. Nucleoside analogs are mutagens

  14. Intercalating agents

  15. UV light as a mutagen

  16. Repair mechanisms • Wrong nucleotide inserted • Proofreading • Mismatch repair

  17. Repair: Mismatch

  18. Repair of UV damage • Two repair mechanisms • Light repair • Dark repair

  19. Why use bacteria to study mutations? Only have one chromosome…one copy of each gene Easy to grow

  20. Direct selection Testing for traits that are easily identified Colony color Motility Resistance to antibiotics

  21. Indirect selection A way to look at traits that are not easily identified, at changes in metabolic pathways Replica plating A way to identify AUXOTROPHS from PROTOTROPHS

  22. Replica Plating: indirect selection

  23. Penicillin enrichment of mutants

  24. Testing chemicals for mutagenicity…Ames test

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