Final answer:
During anaphase, sister chromatids are pulled apart by the shortening of the spindle fibers.
Step-by-step explanation:
During anaphase, the sister chromatids are pulled apart by the shortening of the spindle fibers. This is like reeling in a fish by shortening the fishing line. One sister chromatid moves to one pole of the cell, and the other sister chromatid moves to the opposite pole. At the end of anaphase, each pole of the cell has a complete set of chromosomes.