From pattern to gene, from gene to pattern.

Our understanding of animal development has been revolutionized by genetic approaches to the identification and isolation of pattern-regulating genes. In the past several years, fundamental embryological concepts such as morphogenetic fields, compartments, and organizers have been defined at a molecular level and visualized in developing animals. Here, I will discuss how the focus on the regulation and function of genes with dramatic effects on pattern formation, primarily by through the analysis of gene expression patterns as surrogates of physical pattern elements, has elucidated gene hierarchies that control developmental pathways.