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Hemangioblasts are thought to be one of the sources of hematopoietic progenitors, yet little is known about their localization and fate in the mouse embryo. We show here that a subset of cells co‐expressing the hematopoietic marker GATA‐1 and the endothelial marker VE‐cadherin localize on the yolk sac blood islands at embryonic day 7.5. Clonal analysis demonstrated that GATA‐1⁺ cells isolated from E7.0–7.5 embryos include a common precursor for hematopoietic and endothelial cells. Moreover, this precursor possesses primitive and definitive hematopoietic bipotential. By using a transgenic complementation rescue approach, GATA‐1⁺ cell‐derived progenitors were selectively restored in Runx1‐deficient mice. In the rescued mice, definitive erythropoiesis was recovered but the rescued progenitors did not display multilineage hematopoiesis or intra‐aortic hematopoietic clusters. These results provide …