Testing a hypothesis for chromosome separation during anaphase


(a) In this experiment the kinetochore microtubules are labeled with a fluorescent dye. During early anaphase, a laser is aimed at microtubules about midway between the pole and the kinetochore. The laser eliminates fluorescence at the target region, but the microtubules still function. This treatment marks a fixed point on a microtubule, making it possible to monitor changes in the length of the microtubule.


(b) As anaphase proceeds, the chromosomes move toward the poles, and the segment of microtubule on the kinetochore side of the laser mark shortens. The portion of the tubule on the centrosome side of the mark retains its length. This is one of the experiment supporting the hypothesis that a chromosome tracks along shortening microtubules that depolymerize at their kinetochore ends. (Modified from Campbell, Biology)