Backward chromosome movement in anaphase, after irradiation of kinetochores or kinetochore fibres

Summary We used an ultraviolet microbeam to irradiate kinetochores, or to irradiate kinetochore fibres just in front of kinetochores, in anaphase crane-fly spermatocytes. Forward movements were blocked after most irradiations, but in 7 cells the associated anaphase half-bivalents moved backward, 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 reproducibly.