During Anaphase, which event occurs?

• A. The nuclear envelope breaks up, and kinetochores attach to microtubules
• B. Chromosome line up at the middle
• C. Chromosomes separate and move to opposite ends of the cell
• D. The cytoplasm divides

Answer: (C)

During anaphase, the sister chromatids are separated and pulled toward opposite ends of the cell. This happens after they’ve been held together at the centromere by cohesin proteins; at the start of anaphase these proteins are cleaved, allowing the chromatids to part ways. Kinetochore microtubules shorten, tugging each chromatid toward a pole, while non-kinetochore microtubules lengthen to push the poles further apart, helping to elongate the cell. The nuclear envelope has already broken down earlier in mitosis, so it doesn’t reform yet, and cytokinesis—the division of the cytoplasm—occurs later, at the end of mitosis. Metaphase, by contrast, is when chromosomes line up at the cell’s middle, which is not the event described here.