Abstract
That all higher organisms possess some segmental organization during their development is presumably no coincidence. Segmentation appears to be an important developmental strategy with which to build and diversify different body regions. It can be studied at many levels, ranging from molecule and genome, through cells and their interactions, to morphogenesis and whole body pattern; and there is no compelling reason for thinking that the study of any one level will prove more revealing than that of any other. The study of vertebrate segmentation in fact provides a particularly good example of this philosophy. The application of classical and molecular genetic analysis to Drosophila development (reviewed by Akam, 1987) has yielded a large amount of information about the genes that play a role in the development of segmental patterns in this organism. Springing directly from this analysis comes the hope that similar methods applied to vertebrate development, exemplified by the discovery of the homeobox in the vertebrate genome, will be just as successful. But will the identification of vertebrate segmentation genes complete our understanding of the segmentation process? We believe not, and our chief purpose in this review is to identify and discuss the variety of different levels at which one can approach the major events involved.
