Figure 3.

(A) Nicklas used a glass needle to apply force on anaphase chromosomes and slowed their motion. (B) He characterized the relationship between the applied force and velocity using a force–velocity curve. When no force is applied, the chromosomes move at the spindle’s preferred speed. Since the spindle has a preferred speed, it contains a speed governor. The stall force is the applied force that causes the chromosomes to stop moving. The origin of the speed governor in the spindle remains unclear, and, as will be elaborated on in Section 4, it might not reflect the force-generating properties of the kinetochore.