Mitotic spindle assembly checkpoint protein MAD1 is a protein that in humans is encoded by the MAD1L1 gene. It is mapped to 7p22.3. MAD1L1 is a component of the mitotic spindle-assembly checkpoint that prevents the onset of anaphase until all chromosome are properly aligned at the metaphase plate. MAD1L1 can function as a homodimer. It localizes to the centrosome during metaphase and to the spindle midzone and the midbody during anaphase and telophase. MAD1L1 may also play a role in cell cycle control and tumor suppression.