Malorientation and abnormal segregation of chromosomes during recovery from Colcemid and Nocodazole

Reversal of meiotic arrest in crane‐fly spermatocytes by U.V. irradiation of Colcemid‐arrested cells or by rinsing Nocodazole‐arrested cells in fresh buffer results in the induction of chromosome malorientation. Malorientations observed among Colcemid‐recovering and Nocodazole‐recovering spermatocytes at frequencies higher than normally observed in untreated cells included associations of sister kinetochores of half‐bivalents with both spindle poles (amphitely), in contrast with associations of sisters with only one pole (syntely) as is usually found during the first meiotic division. In several cases, prior to anaphase onset, maloriented bivalents appeared unusually tilted with respect to the spindle axis, and during anaphase they gave rise to laggard half‐bivalents that did not segregate during anaphase along with half‐bivalents having proper syntelic orientation. The results parallel previous findings obtained during cold recovery, and the properties of the drugs used here suggest that their action on microtubules, although reversible, induces malorientation during recovery from meiotic arrest.