Homologous chromosome pairs are bound together through recombination-derived cross-over events, forming a bivalent. During prometaphase and metaphase, the SAC is active due to a lack of microtubule–kinetochore attachment and/or tension between the bivalent and microtubules. During SAC activation, Mps1 is recruited to unattached kinetochores leading to further recruitment of Bub1, Bub3 and BubR1. Mad1 and Mad2 are also directly recruited to the kinetochore. Mad2 undergoes a conformational change, which promotes the formation of the potent APC inhibitor MCC in the cytoplasm. The kinetochore protein Ndc80 (Hec1) binds directly to microtubules to promote microtubule–kinetochore attachment and also the recruitment of Mad1 to kinetochores. Spc24 and Spc25 are other kinetochore proteins which regulate SAC activation through the recruitment of Mad2. As microtubules attach to kinetochores correctly, tension across the bivalent increases. Insufficient tension can also activate the SAC via Aurora B/C activation and the error correction pathway. At anaphase, the bivalents are separated by the cleavage of cohesin by separase, but centromeric cohesin holding the chromatids together is protected. Sgo2 inhibits separase activity at the centromeric region. Mps1 and Bub1 ensure the correct localization of Sgo2. Esco2 is a cohesin-producing enzyme which is also essential for SAC activation. If Esco2 activity is not sufficient, SAC is not activated when required therefore proteins such as Bub1 are mislocalized. The cohesin subunit Smc1B is also necessary for SAC activation.