Chromosome mis-segregation and aneuploidy in somatic cells is an extremely rare event due to the cellular machinery in place to prevent it. The main player in ensuring chromosomes segregate properly during anaphase of mitosis is called the spindle assembly checkpoint. SAC is only silenced when amphiletic attachment of kinetochores to microtubules has occurred and anaphase commences. If incorrect attachment has occurred, SAC is turned on and recruits a host of different proteins including those of the MAD and BUB family, which catalyze the inhibition of APC/C that keeps the cell in metaphase. This highly conserved machinery leads to segregation with great fidelity.
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