KINETOCHORE MICROTUBULES AND CHROMOSOME MOVEMENT DURING PROMETAPHASE IN DROSOPHILA-MELANOGASTER SPERMATOCYTES STUDIED IN LIFE AND WITH THE ELECTRON-MICROSCOPE

Prometaphase I chromosome behavior was examined in wild-type Drosophila melanogaster primary spermatocytes. Cine analysis of live cells reveals that bivalents exhibit complex motions that include (1) transient bipolar orientations, (2) simultaneous reorientation of homologous kinetochores, (3) movements not parallel to the spindle axis, and (4) movement along the nuclear membrane. -Kinetochores and kinetochore microtubule have been anaylzed for bivalents previously studied in life. The results suggest that most chromosome motions (complex though they may be) can be explained by poleward forces acting on or through kinetochore microtubules that span the distance between the kinetochore and the vicinity of a pole. The results also suggest that the majority of short kinetochore microtubules may be remnants of previous microtubule-mediated associations between a kinetochore and a pole.