Coincident recombination during mitosis in saccharomyces: distance-dependent and -independent components

In mitosis, coincident recombination events between widely separated markers occur more frequently than expected for two independent acts. Several different mechanisms have been proposed to account for this phenomenon. It has been argued that coincident recombination could be due to either an extensive region of heteroduplex DNA or some other distance-dependent mechanism. Alternately, it has been suggested that at least some is due to subpopulations of cells which undergo recombination at very high frequencies. The purpose of these experiments is to evaluate the possible contribution of distance-dependent and distance-independent components. By comparing the coincident recombination frequencies for markers on the same homolog as well as pairs of unlinked sites, we show that there is a strong distance-dependent component for at least 8.8-35-kbp, depending on the type of recombination event (conversion or intrachromosomal exchange). For larger distances separating sites, a distance-independent mechanism(s) results in higher than expected frequencies.