Development, evolution, and corroboration

The cloning of genes involved in pathways fundamental to morphogenesis has opened the door to visualizing expression of developmental regulatory genes in many organisms. Expression data have become technical commonplace in an alysis of mutants of Drosophila melanogaster and a handful of other genetic model systems. Many researchers have used probes and extended the logic fr om studies of D, melanogaster for comparisons of expression patterns to inf er developmental bases for homologous structures among animals with diverse body plans. This research program has led to exciting but sweeping general izations about how development evolves. Here we examine several underlying assumptions of this approach in terms of comparative and historical biology . First, we evaluate the logic that underlies the equation of gene expressi on similarity with homologous morphology. Second, we examine epistemologica l issues surrounding the descriptive visualization of gene expression patte rns. We conclude by examining the role of phylogenetic coding and mapping o f these patterns to examine the evolution of complex gene regulatory networ ks. Anat Rec. (NewAnat.): 257:6-14, 1999. (C) 1999 Wiley-Liss, Inc.