During which phase of mitosis do chromatids separate and begin to move to opposite poles?

During mitosis, the phase where chromatids separate and move towards opposite poles is Anaphase. This phase follows Metaphase, where chromosomes are lined up at the cell's equatorial plane. During Anaphase, the cohesin proteins that hold the sister chromatids together are cleaved, allowing the chromatids to be pulled apart by the spindle fibers attached to the kinetochores. As the microtubules shorten, the separated chromatids, now individual chromosomes, are drawn towards opposite ends of the cell. This movement is crucial for ensuring that each daughter cell will receive an identical set of chromosomes when the cell ultimately divides.

As a subsequent step, Telophase, following Anaphase, involves the reformation of the nuclear envelope around each set of chromosomes, but it does not involve the separation of chromatids.