A replication model for sister-chromatid exchange

A model for the production of sister-chromatid exchanges is presented, based on the idea that double-strand breaks are generated at junctions between a completely duplicated replicon cluster and a partially duplicated replicon cluster. Agents that induce absolute blocks to DNA fork displacement will cause this condition to persist longer than normal, whereas agents that inhibit initiation of whole clusters will rarely cause it at all. During the blunt-end repair of the double-strand breaks, sister-chromatod exchange would be initiated when daughter strands of a duplicated cluster recombine with the parental strands of the partially replicated cluster. When the latter finishes replication, sister-chromatid exchange would be completed.