Erich A Nigg1, Cesar Martins2. 1. Biozentrum, University of Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland. erich.nigg@unibas.ch. 2. Department of Morphology, Institute of Biosciences, UNESP São Paulo State University, Botucatu, 18618-689, SP, Brazil.