BACKWARD CHROMOSOME MOVEMENT IN ANAPHASE, AFTER IRRADIATION OF KINETOCHORES OR KINETOCHORE FIBERS

We used an ultraviolet microbeam to irradiate kinetochores, or to irra diate kinetochore fibres just in front of kinetochores, in anaphase cr ane-fly spermatocytes. Forward movements were blocked after most irrad iations, but in 7 cells the associated anaphase half-bivalents moved b ackward, toward their partner half-bivalents, with speeds faster than poleward movements. The occurrence of backward movement suggests that there may be mechanical connections between separating half-bivalents. We have been unable to find conditions to obtain these results reprod ucibly.