Abstract: During development, cells in an embryo face two major tasks. First, they must express distinct combinations of genes appropriate for specific cell fates such as muscle and skin. Once such patterns of gene expression are established, cells must change their shape and position to match those cell fates. These morphological transformations are remarkable for their speed and precision, but also for their incredible beauty. The associated cell-shape changes depend on local patterns of gene activity, but how such patterns are converted into the physical properties controlling shape and motility is a major unanswered question in biology. In my talk, I will describe my lab’s attempts to address these questions using the Drosophila embryo as a model system. A surprising feature of these morphological changes is that although they are driven by gene activities in individual cells, they can often be understood as global changes in the distribution of physical forces within the entire tissue. These findings open up a new perspective on the relationship between cells and organismal morphology. Biosketch: In the late 1970s, Eric Wieschaus and Christiane Nüsslein-Volhard carried out large-scale mutagenesis screens to identify genes controlling embryonic development in Drosophila. In contrast to previous genetic analyses, these screens were designed for genomic saturation, i. e.; identifying key components in all pathways governing morphology, patterning and differentiation. These experiments established a basic “tool box” of maternal factors and signaling pathways that operate in the Drosophila embryo and are conserved with remarkable fidelity in all multicellular organisms including humans. Mutations in the associated genes account for a significant fraction of inherited birth defects in humans and play a major role in cancer. Wieschaus and collaborators went on to elucidate basic features of the Wnt pathway. More recent work focuses on the mechanics of cell shape change and movement during gastrulation and on biophysical measurements of gradients and transcriptional activation during early development. In 1995, Wieschaus was the recipient of the Nobel Prize in Physiology or Medicine. The ICTP Colloquium will take part at the end of the Winter School on Quantitative Systems Biology, from 5-16 December 2016, (smr 2879). For information on the Winter School see: http://indico.ictp.it/event/7661/