Anaphase

Anaphase is the third stage of mitosis, following metaphase. At the end of metaphase each chromosome, made of two identical sister chromatids joined at the centromere, is lined up on the equator of the spindle with spindle fibres attached to its centromere.At the start of anaphase the centromeres divide, so the two sister chromatids of each chromosome separate. From this point each chromatid is treated as a separate daughter chromosome.The spindle fibres attached to the centromeres shorten, pulling the chromatids towards opposite poles of the cell. The centromere leads, so the arms of each chromatid trail behind, giving the characteristic V shape seen under the microscope. The energy for this movement comes from ATP, supplied by respiration in mitochondria.Because the two chromatids of each chromosome are genetically identical copies made by DNA replication during interphase, each pole receives one complete set of chromosomes, identical to the set at the other pole. In a human cell, 46 chromatids move to each pole.Anaphase is quick compared with the other stages of mitosis. It ends when the separated chromatids have reached the poles, and telophase begins.A drug that stops spindle fibres forming, such as colchicine, stops cells at metaphase, because without spindle fibres the chromatids cannot be pulled apart.