Netter's Anatomy Practice Test

Chromosome movement in cell division is driven by the spindle apparatus organized at the centrosome. The centrosome contains a pair of centrioles, each a cylindrical bundle of microtubule triplets. These two centrioles sit at opposite ends of the cell and organize the microtubules that attach to chromosomes at kinetochores, pulling sister chromatids toward opposite poles during mitosis. The centrioles duplicate before division so two poles form, creating the bipolar spindle necessary for accurate chromosome separation. The nucleolus is focused on ribosome production, not spindle formation; microtubules are the fibers that form the spindle but are not paired, bundle-like inclusions themselves; organelles is a broad term that does not specify the structure responsible for organizing the spindle.