“…Our results show that there is a difference between the two mei-9 alleles with respect both to rod chromosome magnification and ring chromsome transmission under magnifying conditions: mei-9" strongly inhibits both rod X*" chromosome magnification and ring X"" chromosome transmission under magnifying conditions, while mei-9" has a smaller inhibitory effect on rod chromosome magnification and on the transmission of ring chromosomes under magnifying conditions. Our results confirm the report by Polito et al (1982) that mei-9 a inhibits magnification and demonstrate that mei-9" has a small, but detectable, inhibitory effect on magnification. The observation that mei-9", which has been characterized as normal in post-replication repair but defective in excision repair (Boyd, Golino & Setlow, 19766) and repair replication (Nguyen & Boyd, 1977), and mei-9", which is defective in repair replication (Nguyen & Boyd, 1977), inhibit magnifying events suggests that a component of the excision repair pathway is involved in rDNA magnification.…”