Requirement of the spindle checkpoint for proper chromosome segregation inbudding yeast meiosis

The spindle checkpoint was characterized in meiosis of budding yeast. In th e absence of the checkpoint, the frequency of meiosis I missegregation incr eased with increasing chromosome Length, reaching 19% for the longest chrom osome. Meiosis I nondisjunction in spindle checkpoint mutants could be prev ented by delaying the onset of anaphase. In a recombination-defective mutan t (spo11 Delta), the checkpoint delays the biochemical events of anaphase I , suggesting that chromosomes that are attached to microtubules but are not under tension can activate the spindle checkpoint. Spindle checkpoint muta nts reduce the accuracy of chromosome segregation in meiosis I much more th an that in meiosis II, suggesting that checkpoint defects may contribute to Down syndrome.