Pathways of over-replication. The G1 state required for coordinated origin licensing is normally reached by passing through mitosis. Endoreduplicating cells reach G1 from early M (a), G2 (b) or S (c). Re-replication (d) involves a continuous S-phase during which origin licensing and firing are both permitted. Endomitosis (e) occurs when cytokinesis (CyK) is bypassed but does not involve premature licensing. This figure is similar to Fig. 3 in  describing naturally occurring endoreduplication. Pro, Met, Ana, Tel refer to prophase, metaphase, anaphase and telophase, respectively.