Molecular biology of development. Introductory comments.

Abstract

For many centuries, a central question in developmental biology has been how a fertilized egg with little apparent internal organization is so quickly converted, without external instructions, into a highly organized functional larva. This question only became accessible to concerted experimental analysis toward the end of the 19th century, when, as in most areas of science, progress was limited much more by available methods than by concepts. Until about 100 years ago, analysis was largely restricted to descriptive cytology; as can be seen from the justly celebrated volume of E.B. Wilson (1925), the precision of descriptive detail at the light microscope level has not been surpassed today. Since 1900, methods of embryological intervention have been much the same as those that are used today with greater sophistication. These include egg centrifugation (or rotation), hair-loop constriction, blastomere separation and their culture in isolation, blastomere or tissue transplantation, and the...