"Much of what we know about how embryos determine their axes of symmetry comes from research in invertebrates (mainly Drosophila) and cold-blooded vertebrates (mainly Xenopus). In both cases, polarity is set up by the localisation of maternal determinants in the cytoplasm of the fertilised egg. These determinants are inherited differentially by daughter cells, leading them to acquire different fates, which effectively fixes the axes of the embryo by the 8 cell stage. In contrast, in amniotes (reptiles, birds and mammals) embryonic polarity remains plastic until much later, just before gastrulation, when the embryo may contain as many as 50,000 cells. If an embryo at this stage is cut into fragments, each fragment can generate a complete embryo. This property, called "embryonic regulation", is thought to be responsible for the generation of monozygotic (identical) and conjoined ( Siamese ) twins in humans and other amniotes. We know almost nothing about how polarity is determined in higher vertebrates or about the mechanisms of embryonic regulation and twinning. This project uses a multi-disciplinary systems approach to reveal the gene interaction network controlling polarity, regulation and twinning. The project will also generate a mathematical model of early development or "virtual embryo", allowing prediction of experimental outcomes and clinical scenarios."