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CHAPTER 10 Homologous recombination at the molecular level

CHAPTER 10 Homologous recombination at the molecular level. 1.All DNA is recombinant DNA. 2.Genetic exchange works constantly to blend and rearrange chromosomes, most obviously during meiosis, when homologous chromosomes pair prior to the first nuclear division.

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CHAPTER 10 Homologous recombination at the molecular level

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  1. CHAPTER 10 Homologous recombination at the molecular level

  2. 1.All DNA is recombinant DNA. 2.Genetic exchange works constantly to blend and rearrange chromosomes, most obviously during meiosis, when homologous chromosomes pair prior to the first nuclear division. 3.During this pairing, genetic exchange between the chromosomes occurs. This exchange, classically termed crossing over, is one of the results of homologous recombination.

  3. OUTLINE • Models for Homologous Recombination • Homologous Recombination Protein Machines • Homologous Recombination in Eukaryotes • Mating-Type Switching • Genetic Consequences of the Mechanism of Homologous Recombination

  4. Two models for Homologous Recombination • 1.The Holliday Model • 2.The Double-Strand Break Repair Model

  5. The Holliday Model Illustrates Key Steps in Homologous Recombination 10-1 Holliday model through the steps of branch migration

  6. 10-2 Holliday junction cleavage

  7. Key words of Holliday Model • Holliday junction • Branch migration • Heteroduplex DNA • Crossover product • Patch product

  8. The Double-Strand Break Repair Model More Accurately Describes Many Recombination Events 10-3 DSB repair for homologous recombination

  9. Duble-Stranded Breaks Arise by Numerous Means and Initiate Homologous Recombination

  10. 3.Homologous recombination protein machines

  11. The RecBCD Helicase/Nuclease Processes Broken DNA Molecules for Recombination 10-5 Steps of DNA processing by RecBCD

  12. RecA Protein Assembles on Single-stranded DNA and Promotes Strand Invasion 10-6 Substrates for RecA strand exchang

  13. 10-7 Polarity of RecA assembly

  14. Newly Base-Paired Partners Are Established Within the RecA Filament RecA Homologs are present in all organisms

  15. Other Proteins • RuvAB Complex Specifically Recognizes Holliday Junctions and Promotes Migration • RuvC Cleaves Specific DNA Strands at the Holliday Junction to Finish Recombination

  16. Homologous Recombination In Eukaryotes • Homologous Recombination Has Additional Functions in Eukaryotes • Homologous Recombination Is Required for Chromosome Segregation during Meiosis(nondisjunction,meiotic recombination) • Programmed Generation of Double-Stranded DNA Breaks Occurs during Meiosis(Spo11 protein )

  17. 10-8 DNA dynamics during meiosis

  18. 10-9 Mechanism of cleavage by Spo11

  19. MRX Protein Processes the Cleaved DNA Ends for Assembly of the RecA-like Strand-Exchange Proteins • Dmc1 Is a RecA-like Protein that Specifically Functions in Meiotic Recombination • Many Proteins Function Together to Proote Meiotic Reconbination (recombination factories)

  20. 10-10 Overview of meiotic recombination pathway

  21. 10-11Dmc1-dependent recombination occurs preferentially between nonsister homologous chromatids

  22. Mating-Type Switching 10-12 Genetic loci encoding mating-type information

  23. Mating-Type Switching Is Initiated by a Site-Specific Double-Strand Break (HO endonuclease ) • Mating-Type Switching Is a Gene Conversion Event, Not Associated with Crossing Over(SDSA)

  24. 10-13 Recombination model for mating-rype switching:synthesis-dependent strand annealing (SDSA)

  25. Genetic Consequences of the Mechanism of Homologous Recombination • Exchang or Conversion • Gene Conversion Occurs because DNA Is Repaired during Recombination

  26. 10-14 Comparion of the genetic and physical maps of a typical region of a yeast chromosome

  27. 10-15 Mismatch repair of heteroduplex DNA within recombination intermediates can give rise to gene conversion

  28. The end 生物学基地班 200431060053.田小俊

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