The External mechanics of the chromosomes V—The balance theory of mitosis

Abstract

In the present studies, material of Fritillaria has been used to show the effect of different variables on the external movements of the chromosomes. The first shows the effect of different time-relationships at meiosis on the localization of pairing. The second shows the effect of the body-repulsions on the metaphase arrangement of bivalent chromosomes. The third shows the effect of the centromere-repulsions on the metaphase arrangement of trivalents and their relationship with the polar repulsions and the axial orientation of the spindle particles. The fourth shows the effect of varying the polar repulsions, by varying the time coordination of centrosomes (or spindle-pole determinants) and chromosomes, on the metaphase arrangement at mitosis and meiosis. These and more general observations in other material are the main sources of evidence that I want to consider in relation to the external mechanics of the chromosomes. It is impossible to describe here the evidence of every kind of force working on every kind of chromosome configuration at every stage of development. To do so would make the material unwieldy. We should not be able to see the wood for the trees. Nor is it yet possible to deal thoroughly with those special types of mitosis found in the Protista or those exceptional types of meiosis described by the Schraders (1931, 1932) and by Metz, Moses, and Hoppe (1926), since the general rule must be understood before the exceptions can be explained. I therefore propose to consider merely that great body of plants and animals which seems to obey certain consistent rules at meiosis and mitosis.