Defining the boundaries of zebrafish developmental genetics.

The first systematic, functional screens to identify the genes involved in vertebrate embryogenesis have been completed in the zebrafish, Danio rerio. In an extraordinary issue of the journal Development, devoted entirely to the results of these screens, over 500 mutant loci, many with multiple alleles, are described and classified according to the phenotypes they produce. Each class defines a small number of genes that act together to determine the proper development of many features of vertebrate anatomy, from the determination of body plan to the development of discrete organs and cell types.