The skeleton, tendons, and glands of a functional jaw all derive from the same population of stem cells, which arise from a cell population known as neural crest. To discover how these neural crest-derived cells know to make the right type of cell in the right location, researchers focused on a particular gene, Nr5a2, that was active in a region of the face that makes tendons and glands, but not skeleton. To understand the role of Nr5a2, the scientists created zebrafish lacking this gene. These mutant zebrafish generated excess cartilage and were missing tendons in their jaws.