a, Single-cell traces of CDK2 activity after siRNA knockdown of cyclins D1, D2 and D3 (combined), siRNA knockdown of p21, or control siRNA. b, c, Chemical-induced rapid expression of cyclin D1 or p21 controls the CDK2 paths in daughter cells. b, Schematic of chemical-induced DHFR-mCherry-cyclin D1 or DHFR-mCherry-p21 constructs. c, CDK2 activity traces aligned to the time of mitosis. Only cells that were treated with DMSO, 0.05 μM TMP or 5 μM TMP 1–5 h before mitosis (marked in yellow) were selected for plotting. Note that TMP was not washed out (marked in grey).