The schema shows the available switchpoints from the mitotic pathway to the endocycle in p53 mutant cells and stimulation of this switch by DNA damage. As can be seen, G2 arrested cells can go directly from the G2/M damage checkpoint into the endocycle or go on to apoptose. However, if the G2/M checkpoint is adapted, cells can also enter into mitosis, and from there possible arrest in metaphase. In turn, M-arrest has three alternative exits: to return to the mitotic cycle, to undergo apoptosis or, through restitution, to enter the endocycle. Mitosis restitution is unstable and can be aborted evoking apoptosis. Endocycling cells often precipitate apoptosis, but can also return through somatic reduction to the mitotic cycle. The checkpoint(s) for this last process is unknown.