Anaphase is the phase where the chromosomes start to seperate because proteins in the kinetochore, which are located near the centromere moving to the MTOCs with help of ATP. Also, some mitotic spindles are attached to the chromosones and they start to shorten, dragging thier chromosones towards oppossite ends of the cell. However, not all spindles are attached to chromosomes, and the ones that aren't lengthened and elongate the cell.