Biochemical Systematics and Ecology 27 (1999) 117 — 129 The use of isozyme characters in systematic studies Donald G. Buth* and Robert W. Murphy  Department of Biology, University of California (UCLA), Box 951606, 621 Circle Drive South, Los Angeles, CA 90095-1606, USA  Centre for Biodiversity and Conservation Biology, Royal Ontario Museum, 100 Queen+s Park, Toronto, Ont., Canada M5S 2C6 Received 16 January 1998; accepted 19 February 1998 Abstract Several classes of isozyme characters are recognized including the number of genes that control a given enzyme system, intralocus and interlocus heteropolymer assembly, tissue- specific gene expression, developmental patterns of enzyme expression, and post-translational modification of gene products. All of these characters can be of value in systematic studies although few applications have been made to date; some of the more robust examples are recognized. Isozyme characters should be evaluated in terms of both their advantages and limitations. The level of universality at which they are used is group-specific. Tissue-specific gene expression data may be of the widest applicability in systematic studies.  1999 Elsevier Science Ltd. All rights reserved. Keywords: Isozymes; Number of genes; Gene expression; Heteropolymer assembly; Post-translational modification 1. Introduction In systematics, the information generated by the starch gel electrophoresis (SGE) of enzymes (including polyacrylamide PAGE and cellulose acetate CAGE; Richardson et al., 1986; Murphy et al., 1996) has become synonymous with allozymic data (e.g. Ayala, 1983). The historic pathway from the first development of this technology to applications in systematic biology has been indirect, and several subdisciplinary ‘‘filters’’ have narrowed the potential of the information that could be obtained. It is * Corresponding author. Fax: (310) 206 3987; e-mail:dbuth@UCLA.edu. 0305-1978/99/$ — See front matter  1999 Elsevier Science Ltd. All rights reserved. PII: S0305-1978(98)00052-0