What is the main action that occurs during anaphase?

During anaphase, the defining action is the separation of sister chromatids, which occurs as the spindle fibers exert force to pull them apart. This stage of cell division is critical because it ensures that each daughter cell receives an identical set of chromosomes. The spindle fibers, which are formed from microtubules, attach to the centromeres of the chromosomes and contract, effectively dragging the sister chromatids toward opposite poles of the cell.

This separation is essential for maintaining the correct number of chromosomes in the resulting daughter cells. After anaphase, each side of the cell will contain an equal set of chromosomes, preparing for the subsequent stages of cell division, such as telophase and cytokinesis. The other options represent different stages of the cell cycle or actions that occur at other phases, not during anaphase.