Curr Opin Genet Dev,
This issue of Current Opinion in Genetics and Development examines mechanisms by which pattern is established during the development of a broad range of organisms and in a wide variety of tissues. Perhaps the most important message to emerge is that, on the whole, developmental mechanisms have been extraordinarily well conserved during evolution. Each embryo appears to have at its disposal a fundamental 'toolkit' of regulators and regulatory pathways with which to construct an organism. Most chapters in this issue discuss the tools; the last chapter, by contrast, addresses the evolutionary question of how different embryos give rise to distinct organisms with essentially the same 'tool-kit' of molecules during development.