RESUMO
The transformation of embryology to developmental biology has been linked to the introduction of experimental approaches from molecular genetics to the study of development. This paper pursues this theme by analyzing the tools molecular biologists, moving from phage and bacterial genetics to the study of development in higher organisms, brought to their new field of investigations. The paper focuses on Sydney Brenner's move from molecular genetics to developmental biology. His attempt to turn the nematode worm Caenorhabditis elegans into a new tool for the study of development included a vast and ever expanding mapping program. Worm workers themselves did not distinguish sharply between mapping on the cellular, chromosomal or molecular level. Mapping, the paper argues, or more generally 'analytical/comparative' next to 'experimentalist' approaches (Pickstone) were not only part and parcel of Brenner's strategy to 'molecularize' the study of development, but also played a crucial role in 'classical' molecular biology.