cytokinesis

Meaning: Cytokinesis divides the cytoplasm and plasma membrane, producing two daughter cells. It usually begins in late anaphase or telophase, once the chromosomes have separated. In animal cells, a ring of actin and myosin filaments under the membrane contracts and pinches the cell in two, forming a cleavage furrow. Plant cells have a rigid wall, so Golgi-derived vesicles fuse at the midline to build a cell plate that becomes the new wall. Cytokinesis also follows meiosis, and in oogenesis it is unequal, giving one large cell and small polar bodies.

On the MCAT: A passage may describe a drug or mutation that disrupts actin or myosin. Predict that the nucleus can still divide but the cell does not, giving a binucleate or multinucleate cell. Questions may also ask which cytoskeletal element does the work: microfilaments for the contractile ring, microtubules for the spindle.

Common confusion: Cytokinesis is not the same as mitosis. Mitosis is division of the nucleus (chromosome segregation), while cytokinesis divides the cytoplasm. They are normally coupled in the M phase, but nuclear division can occur without cytokinesis.