A simple model for the metaphase-to-anaphase transition in adaptation. (A) APC/C^Cdc20, Cdc28/Clbs, and PP2A^Cdc55 give rise to a positive feedback loop (PFL) and a negative feedback loop (NFL). (B) The dynamics of the model are shown starting from the lowest Clb2 levels in both a regular transition to anaphase (solid line) and during adaptation (broken line; decreased activation rate of APC). See also Materials and methods.