Phase-contrast Cinematographic Studies on Meiosis in Orthopteran Spermatocytes
II. Chromosomal movement in the first meiotic anaphase
1960 年 25 巻 3-4 号 p. 293-304
詳細
1960 年 25 巻 3-4 号 p. 293-304
Phase-contrast cinematography was used for the study on the meiotic processes from metaphase I to telophase I in the spermatocytes of several species of grasshoppers, obtaining the following results.
1) The chromosome separation and the changes in spindle and cell diameters in anaphase I were measured on the cine-films. The graph of chromosome separation plotted against time was S-shaped in each spermatocyte examined. In the anaphase the chromosomes approach the spindle poles, while the spindle body elongates definitely, the two processes occurring almost simultaneously.
2) The continuous spindle fibers were clearly observable in the living, anaphasic cells. So these component fibers of the spindle exist in vivo as a morphological reality and are not an artificial product. Furthermore, it was conjectured that the elongation of the continuous fibers results in stretching the spindle in anaphase.
3) The kinetochore paths of the bivalents were followed from metaphase I to the end of anaphase I on the cine-films. They are grouped into two types: i) in which the kinetochores approach to the spindle axis progressively from the start of anaphase to the complete separation of the chromosomal tips, and ii) in which they approach to the spindle axis after moving parallel to or receding a little from the axis at the start of anaphase. In both the types, the kinetochores recede somewhat from the axis just after the separation of the chromosomal tips and then, they move more or less parallel to the spindle axis, till they deviate towards the spindle pole at the end of anaphase.
4) All the results mentioned above seem qualitatively well explained on the following assumption: an autonomous terminalization of the chiasmata is active at the early anaphase I, the chromosomes are carried to the spindle poles by the traction of the chromosomal fibers and the elongation of the spindle, and the chromosomes are affected in the spindle by a force which tends to push them out of the spindle and/or by a body repulsion among them.
