In normal Drosophila melanogaster oocytes, meiosis arrests at metaphase I and resumes after oocyte passage through the oviduct. Thus, metaphase arrest defines a control point in the meiotic cell cycle. Metaphase arrest only occurs in oocytes that have undergone at least one meiotic exchange. Here it is shown that crossovers between homologs attached to the same centromere do not induce metaphase arrest. Hence, exchanges induce metaphase arrest only when they physically conjoin two separate kinetochores. Thus, the signal that mediates metaphase arrest is not the exchange event per se but the resulting tension on homologous kinetochores.
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