In the next stage of mitosis, called anaphase, the sister chromatids separate (see Fig. 11.5). The centromere holding a pair of sister chromatids together splits, allowing the two sister chromatids to separate from each other. After separation, each chromatid is considered to be a full-fledged chromosome. The spindle microtubules attached to the kinetochores gradually shorten, pulling the newly separated chromosomes to the opposite poles of the cell.

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This event is the basis for the equal segregation of chromosomes between the two daughter cells. During S phase in a human cell, each of the 46 chromosomes is duplicated to yield 46 pairs of identical sister chromatids. Thus, when the chromatids are separated at anaphase, an identical set of 46 chromosomes arrives at each spindle pole, the complete genetic material for one of the daughter cells.