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 cross-overs 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.