Cytokinesis is the process where the cytoplasm of a single eukaryotic cell is divided to form two daughter cells. It usually initiates during the late stages of mitosis, and sometimes meiosis, splitting a binucleate cell in two, to ensure that chromosome number is maintained from one generation to the next.
Animal cell cytokinesis begins shortly after the onset of sister chromatid separation in the anaphase of mitosis. A contractile ring, made of non-muscle myosin II and actin filaments, assembles in the middle of the cell at the cell cortex, adjacent to the cell membrane. Myosin II uses the free energy released when ATP is hydrolyzed to move along these actin filaments, constricting the cell membrane to form a cleavage furrow. Continued hydrolysis causes this cleavage furrow to move inwards, a striking process that is clearly visible down a light microscope.