Which phase of cell division is characterized by the separation of sister chromatids?

The phase of cell division characterized by the separation of sister chromatids is Anaphase. During Anaphase, the cohesion proteins that hold the sister chromatids together are cleaved, allowing the chromatids to be pulled apart by the spindle fibers towards opposite poles of the cell. This separation ensures that each new daughter cell will receive an identical set of chromosomes, thus maintaining genetic fidelity during cell division.

In contrast, Prophase involves the condensation of chromatin into visible chromosomes, and the formation of the mitotic spindle begins, but the chromatids remain attached. During Metaphase, the chromosomes align at the cell's equatorial plane, but they have not yet separated. Telophase marks the end of mitosis when the separated chromatids, now individual chromosomes, reach the poles and the nuclear envelope begins to reform around each set of chromosomes, but separation has already occurred by this point. Thus, Anaphase is the distinct phase where sister chromatids are actively separated and moved towards opposite sides of the cell.