Concluding Comments

Many other examples of this phenomenon could be cited, but the key points to emphasize are that genes are the primary regulators of developmental processes, their protein products function in developmental genetic pathways, and these pathways are employed in related developmental processes in a number of organ systems. Understanding the molecular basis of gene function, how those functions are organized into modules, and how abnormalities in those modules cause and correlate with malformations and pleiotropic syndromes forms the basis of the modern clinical approach to human birth defects. The understanding of these developmental pathways in great detail may also provide an avenue in the future to devise therapies that target appropriate parts of these pathways.