SID1-1: a mutation affecting meiotic sister-chromatid association in yeast.

Meiotic chromosome segregation must occur with high fidelity in order to prevent the generation of deleterious aneuploidies. In meiosis I, homologous chromosomes pair, then migrate to opposite poles of the spindle. This process uses a collection of unique structures and mechanisms that have yet to be thoroughly characterized. To acquire a collection of informative meiotic mutants, we carried out a novel genetic screen in Saccharomyces cerevisiae. This screen was designed to identify dominant mutants in which meiosis I chromosome segregation occurs with decreased fidelity. One mutant recovered using this screen, SID1-1 (sister disjunction), showed an incidence of spores disomic for a marked chromosome III that was 25-fold greater than the wild-type level. Crossing-over is slightly, but not dramatically, reduced in SID1-1. Both recombinant and nonrecombinant chromosomes segregate with reduced fidelity in the presence of SID1-1. We present evidence that the mutant is defective in sister-chromatid association.