1. Homologous Recombination
Exchange between pair of homologous DNA segments
Genetic exchange during meiosis
DNA repair

2. Strand Invasion
Base pairing between complementary strands of two different duplexes
Heteroduplex

3. RecA Protein Catalyzes Strand Invasion
Associates invading strand with DNA duplex being invaded
Transient three-stranded structure
Heteroduplex formation

4. Double Strand Break Repair
Associated sister chromatids
Strand invasion by broken chromosome
DNA synthesis using unbroken chromosome as template

5. Meiotic Recombination
Double-strand break
Strand invasion
Holliday junction
Resolution either regenerates original duplexes or generates crossover

6. Holliday Junction
Isomerization
Resolution by cutting strands

7. Gene Conversion Divergence in allele distribution
Occurs at sites of DNA synthesis following strand invasion and heteroduplex region at crossover sites
Mismatch repair at heteroduplex

8. Preventing Inappropriate Homologous Recombination
Potential recombination between repeated sequences
Aborted due to excessive mismatch
Deletions or gene conversions if allowed to occur

9. Site-specific Recombination
Mobile genetic elements:
moved to nonhomologous sites
encode enzymes that catalyze mobilization
recognition of short sequences at ends

10. DNA-Only Transposons Transposase recognizes sequences at ends
Both ends cut and inserted at new site
Cut-and-paste or replicative pathways

11. Retroviruses RNA genome Reverse transcription (RNA→DNA)
Integration of DNA
Transcription (DNA→RNA)

12. Retroviral-Like Retrotransposons
Retroviral trans-position mechanism
Integration of DNA via RNA intermediate

13. Nonretroviral Retrotransposons
Complex of endonuclease, reverse transcriptase, and transposon RNA nicks target DNA
Free 3’-OH as primer for first strand
Comprise large proportion of human genome