Directionally stable versus unstable kinetochore trajectories in rounded RPE1 cells. (A) Ablation of a single kinetochore (K1) on a bioriented chromosome results in a directionally stable movement of the remaining kinetochore (K2) toward the centrosome (C1). Only low-frequency oscillations (1–2 min periodicity) are evident in the K2 trajectory. (B) Sister kinetochores with laser-severed (K1) versus intact (K2) K-fibers exhibit distinctly different trajectories. Notice that K2 trajectory is smooth, whereas K1 exhibits rapid directional instability. In spite of the severed connection to one spindle pole, the chromosome remains at the spindle equator. Yellow crosses mark the laser beam. Insets are shown at higher magnification. (C) Example of sister kinetochores (K1 and K2) with distinctly different trajectories in an unperturbed RPE1 cell. Notice the high-frequency directional instability in the trajectory of K1.