Gene conversions within the Cup1r region from heterologous crosses in Saccharomyces cerevisiae.

Meiotic recombination among unselected tetrads was analyzed genetically and physically in a heterologous cross where one parent carried six copies of a 1.6 kb CUP1 repeat while the other parent carried seven copies of a 1.1 kb repeat. In the heterologous cross, 140 unselected, complete tetrads were subjected to Southern analysis and 20% exhibited meiotic copy number alterations at the CUP1 locus. Most events, more than 75%, involved only a single spore of a tetrad, and were largely intrachromosomal or sister chromatid events. However, some conversions and associated crossovers between homologs were also observed. We propose that the high level of heterologies interferes with homologous exchanges and leads to an increase in intrachromosomal events.