What occurs during anaphase of mitosis?

During anaphase of mitosis, the critical event that occurs is the separation of sister chromatids, which are the replicated pairs of chromosomes, and their movement towards opposite poles of the cell. This process begins when the cohesion proteins, which hold the sister chromatids together, are cleaved, allowing them to be pulled apart. The spindle fibers, which have attached to the kinetochores of the chromosomes, contract and facilitate the movement of the separated chromosomes toward the spindle poles. This ensures that each daughter cell will receive an identical set of chromosomes when the cell eventually divides.

In contrast, during replication (offered as another choice), chromosomes duplicate during the S phase of the cell cycle before mitosis begins. The reformation of the nuclear envelope takes place during telophase, after the chromosomes have been separated. The dissolution of spindle fibers is not a characteristic event in anaphase; instead, they play a crucial role in facilitating the separation of chromatids throughout this phase. Thus, the movement of chromosomes to opposite ends during anaphase is what defines this stage of mitosis.