The double-strand-break repair model for recombination.

Gene conversion is the nonreciprocal transfer of information from one DNA duplex to another; in meiosis, it is frequently associated with crossing-over. We review the genetic properties of meiotic recombination and previous models of conversion and crossing-over. In these models, recombination is initiated by single-strand nicks, and heteroduplex DNA is generated. Gene conversion is explained by the repair of mismatches present in heteroduplex DNA. We propose a new mechanism for meiotic recombination, in which events are initiated by double-strand breaks that are enlarged to double-strand gaps. Gene conversion can then occur by the repair of a double-strand gap, and postmeiotic segregation can result from heteroduplex DNA formed at the boundaries of the gap-repair region. The repair of double-strand gaps is an efficient process in yeast, and is known to be associated with crossing-over. The genetic implications of the double-strand-break repair model are explored.