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 overlap and slide with respect to each other,effectively shortening the microtubules without depolymerizing the actual fiber.
C)the microtubules elongate and shorten at their kinetochore end.
D)the microtubules are of constant length;centrosomes move farther apart to separate chromosomes.

Question

Quizplus · Accepted Answer

The photobleached sections of the microtubules remaining stationary during anaphase suggests that the microtubules are elongating and shortening at their kinetochore end. This is because the kinetochore is the part of the chromosome that attaches to the microtubules and moves along them during chromosome segregation. If the microtubules were elongating and shortening at their centrosome end, the photobleached sections would still move along with the chromosomes. Option A is incorrect because the photobleached sections remained stationary. Option B is incorrect because there is no evidence of overlapping or sliding of microtubules. Option D is incorrect because the centrosomes moving farther apart cannot account for the movement of the chromosomes along the microtubules.

Once Researchers Understood That Chromosomes Are Moved by the Spindle