Changes of the Chromosomal Spindle (Kinetochore) Fibers and the Behaviour of Bivalent Chromosomes in Grasshopper Spermatocytes After Irradiation of the Kinetochores with an Ultraviolet Microbeam

Abstract

Selected small parts of primary spermatocytes of the grasshoppers, Mongolotettix japonicas and Trilophidia annulata were irradiated with an ultraviolet (UV) microbeam and the subsequent processes in division were followed by phase-contrast and polarization optics. When a kinetochore of a metaphase bivalent was irradiated, the birefringence of the associated kinetochore fiber was lost. Then the bivalent shifted to the pole toward which the other unirradiated kinetochore was oriented. Such a conspicuous shift was not seen when the irradiation was given to a portion of the associated kinetochore fiber alone. The kinetochore-irradiated half-bivalent underwent anaphase movement only when a thin birefringent fiber was reorganized between the irradiated kinetochore and the pole. Frequently, no anaphase movement occurred in the half-bivalent whose kinetochore was irradiated at the end of metaphase. When the kinetochore of a half-bivalent was irradiated in anaphase, the associated kinetochore fiber lost its birefringence, the chromosome continuing to move with some lag. Such a half-bivalent was shown to be pulled poleward by a reduced force. When part of an anaphase kinetochore fiber was irradiated, the motion of the half-bivalent associated with the fiber either did not change or speeded up during the irradiation, the partner half-bivalent being often accelerated.