MAD2L1 also known as MAD2 is a component of the mitotic spindle checkpoint. MAD2L1 plays a critical role in the regulation of the cell cycle, specifically at the mitotic spindle assembly checkpoint, where MAD2L1 ensures proper chromosome segregation. This checkpoint is vital for preventing aneuploidy, a condition that can lead to tumorigenesis. MAD2L1 is localized to unattached kinetochores during prometaphase, where MAD2L1 acts as a sensor for spindle fiber attachment; upon successful attachment, MAD2L1 disassociates, allowing the cell to proceed to anaphase. Notably, cells with mutations in MAD2L1 fail to arrest during mitosis in response to improper spindle assembly, leading to missegregation of chromosomes and potential cell death.