Fig. 6.

Co-occurrence of crossovers in adjacent regions can result in non-crossover recombination. DSBs are formed in the adjacent regions on each of the homologous chromosomes. HR initiates with end resection at the DSBs sites on each of the homologous chromosomes, which produces a 3′ single-stranded end that can invade a homologous template to initiate repair. The second single-stranded end is captured by the D-loop to form a double Holliday junction. The double Holliday junction can be resolved by strand cleavage and result in a crossover (cleavage at arrowheads on one side) outcome (Crossover I and Crossover II). Two double Holliday junctions formed in the adjacent region will result in a four strand recombinant structure. The co-occurrence of crossovers in the adjacent regions would dissolve the Holliday junction of the adjacent DSBs repair intermediates and result in short fragment exchange between the homologous chromosomes (Crossover I + II), looking like a non-crossover recombination event. Arrowheads indicate the cleavage sites