CONSERVATION, DUPLICATION, AND DIVERGENCE OF DEVELOPMENTAL GENES DURING CHORDATE EVOLUTION

Developmental biology has been revolutionised by the discovery that ma ny genes involved in pattern formation, morphogenesis and differentiat ion have been remarkably conserved through evolution. To what extent a re the roles of these genes also conserved? Gene duplication is a majo r factor complicating comparison of developmental genes between diverg ent taxa, since duplication of genes promotes functional divergence. S urveys of homeobox gene diversity in vertebrates and amphioxus reveal that many classes of homeobox genes duplicated close to vertebrate ori gins. This raises the question of how widespread gene duplication was during early vertebrate evolution. We evaluate four lines of evidence for gene duplication in vertebrate evolution: surveys of gene family c omplexity, molecular phylogeny, chromosome mapping and genome size. Th ese suggest that widespread gene duplication occurred close to vertebr ate origins and again during the early gnathostome radiation; the seco nd event may have involved tetraploidy of the genome. We suggest that gene duplication was often followed by the acquisition of new developm ental roles; in this way, duplication may have facilitated the evoluti on of vertebrate body plans. The data imply that unity in developmenta l control between vertebrates and invertebrates will be found in the g eneral properties of each gene family, not in detailed comparisons bet ween individual genes.