During mitosis, sister chromatids pull apart during the anaphase phase.
During anaphase, the paired sister chromatids are separated and pulled toward opposite poles of the cell. This separation is facilitated by the spindle fibers attached to the chromatids at their centromeres. As the spindle fibers shorten, it creates tension that pulls the chromatids apart, ensuring that each new daughter cell will have an identical set of chromosomes. This phase is critical for the accurate distribution of genetic material, preventing any loss or duplication that could lead to cell malfunction or disease.