ABSTRACT Most aspects of chromosome distribution to the daughter cells in meiosis and mitosis are now understood, at the cellular level. The most striking evidence that the proposed explanation is valid is that it correctly predicts the outcome of experiments on living cells in which the experimenter (1) can determine the distribution of any chosen chromosome to a chosen daughter cell, (2) can induce a mal-orientation, and (3) can stabilize a mal-orientation, causing non-disjunction of a chosen bivalent. Recent reviews of chromosome distribution mechanisms are also considered, in an attempt to clarify the remaining unsolved problems.