Patrick Tam is a world leader in the understanding of early mammalian embryonic development. He pioneered novel embryological and genetic manipulation techniques to study the formation of the basic body plan during embryogenesis and the causes of birth defects using mouse genetic models. A significant achievement of his research is the elucidation of the blueprint of development in early mouse embryos and the construction of a complete fate map for the mouse embryo at gastrulation. It is now possible to trace the developmental history and the lineage relationship of any particular group of cells that contribute to the formation of a specific fetal organ or body part.