Increasing Cdk1 activity shortens metaphase. (A) Boxplot (median ± quartiles, X indicates outlier) of metaphase duration in DMSO control or PD-166285–treated cells reveals significant decrease with Wee1 inhibition (P = 0.005, t test, n = 13 control, 7 treated). (B) Boxplot of metaphase duration in cells with or without exogenous Cdc25a demonstrates a significant decrease in metaphase duration with Cdc25a overexpression (P = 0.0008, t test, n = 7 control, 15 cdc25a).