基因 Chapter 19 Homologous and Site-Specific Recombination.pdf

Homologous and Site-Specific Recombination .__ __ - --_._ _._ _-_._-_ _ __ ._-_._._ _-_ .. _-_._--_..-._•._--_..-y•_._.•_ _--_ _ _ •_ _ _ ­ CHAPTER OUTLINE Introduction Pairing and Synaptonemal Complex Formation Are Homologous Recombination Occurs between Synapsed Independent Chromosomes • Mutations can occur in either chromosome pairing or synap­ tonemal complex formation without affecting the other process. • Chromosomes must synapse (pair) in order for chiasmata to form where crossing over occurs. The Bacterial RecBCD System Is Stimulated by chi • We can correlate the stages of meiosis with the molecular Sequences events that happen to DNA. • The RecBCD complex has nuclease and helicases activities. Breakage and Reunion Involves Heteroduplex DNA • It binds to DNA downstream of a chi sequence, unwinds the • The key event in recombination between two duplex DNA duplex, and degrades one strand from 3-5 as it moves to molecules is exchange of single strands. the chi