The main events of the anaphase stage of mitosis are the splitting of the sister chromatids and the moving of them to opposite poles inside the cell. The process begins when the centromeres on each chromosome break, freeing the two halves.
The time this process takes varies depending on the type of organism going through mitosis. The two sister chromatids can move at 0.2 to 0.4 micrometers per minute in a human cell. Spindle fibers and microtubules control the movement of the two halves. The microtubules shorten on one side of the chromatids, pulling them towards the corresponding poles. The polar microtubules lengthen, pushing at the same time. Once the sister chromatids have reached the spindle poles, the microtubules begin to disappear, except for the polar ones. These begin to lengthen, marking the junction between anaphase and early telophase. Late in the anaphase process, the first signs of cytokinesis begin, initially forming the contractile ring. This ring slowly converges until it meets and splits the cell in half.
The process of anaphase has to be triggered. This is done by specific biochemical changes. The protein kinase triggers mitosis and is deactivated by proteolysis of cyclin subunits, triggering the stage of anaphase. There are actually two phases of anaphase. Anaphase I occurs during the shortening of the microtubules. Anaphase II occurs during the lengthening of the polar microtubules and further separation of the spindle poles.