Homologous recombination: single versus double crossovers

(a) Homologous recombination with circular DNA molecule Homology with target gene 2 Plasmid Target gene‘ _ Selectable marker Single crossover at 1 Yeast chromosome Target gene‘ Integrated plasmid l 1 2 1 Target gene' Target gene‘ Single crossover results in integration of introduced DNA without replacement of target gene. Plasmid Target gene' Double crossover at 1 and 2 Yeast chromosome Target gene‘ 1 l 2 Target gene Double crossover results in replacement of target gene. (b) Homologous recombination with linear DNA molecule Single crossover at Selectable marker 1 Linearized plasmid Yeast chromosome I Part of chromosome is lost. Integrated plasmid 1 2 w Target gene’ Single crossover results in integration of introduced DNA ‘ and loss of chromosomes distal to integration site, Double crossover at 1 and 2 Linearized plasmid Yeast chromosome Target gene‘ . i 2 1 Target genes Double crossover results in replacement of target gene.