Once researchers understood that chromosomes are moved by the spindle microtubules, the next question they wanted to answer is how the microtubules function to bring about this process. They used fluorescent labels to make the chromosomes and the microtubular structures fluoresce. When anaphase began centromeres split), they photobleached a section of microtubules. As chromosomes moved toward the poles of the daughter cells, the photobleached sections of the microtubules remained stationary. This result suggests that
A) the microtubules elongate and shorten at the centrosome end.
B) the microtubules elongate and shorten at their kinetochore end.
C) the microtubules are of constant length; centrosomes move farther apart to separate chromosomes.
D) the microtubules overlap and slide with respect to each other, effectively shortening the microtubules without depolymerizing the actual fiber.

Question

Quizplus · Accepted Answer

The fact that the photobleached sections of the microtubules remained stationary while the chromosomes moved suggests that the microtubules are elongating and shortening at their kinetochore end, where they are attached to the chromosomes. This is consistent with previous observations that microtubules "pull" the chromosomes toward the poles of the cell during anaphase.

Once Researchers Understood That Chromosomes Are Moved by the Spindle