A coupling of microtubule dynamics and microtubule motors may keep a chromosome positioned at the equator. (a) The flow of tubulin subunits through kinetochore microtubules can be used to pull or push the chromosome relative to the pole, especially if rapid polymerization or depolymerization occurs at the (+) end of a microtubule. (b) A (−) end – directed motor (dark green) at the kinetochore or a (+) end – directed motor (pink) at the spindle pole can pull a chromosome toward the pole, while CENP-E tethers the kinetochore to a shrinking microtubule. (c) Nonkinetochore microtubules can exert a pushing force on the chromatid arms of a chromosome by polymerization at their (+) ends.