An unattached kinetochore screams “Wait!”

In August of 1993, Conly Rieder and Greenfield “Kip” Sluder skipped a few sessions of the annual Microscopy Society of America meeting in Cincinnati, Ohio, to visit the Air Force museum in Dayton and see the bombers on display. During the drive, they discussed a topic that had been in the back of both of their minds.

Rieder's story began with a 1988 call from Leland Hartwell, shortly before Hartwell had put forward the idea of cell cycle checkpoints (Hartwell and Weinert, 1989). Hartwell asked whether anyone had definitively shown that cells delayed anaphase until all chromosomes were hooked up to the spindle. Rieder noted that there was one obscure abstract concluding that newt cells never started anaphase in the presence of a monooriented chromosome (Zirkle, 1970). And...