A long outstanding problem is the resolution of the full potential of hematopoietic precursors. The commonly used allotypic marker Ly5 permits the tracing of lymphoid and granulocyte-macrophage (GM) output. Here we present a novel eGFP allele that allows the quantitative analysis of red blood cell (RBC) origin at the single-cell level. The miR-144/451 locus is required for erythroid development and homeostasis. Taking advantage of the fact that miR-451 is specifically and highly expressed in the erythroid lineage, we inserted an eGFP expression cassette into the miR-144/451 locus. In miR-144/451(+/eGFP) animals, accumulation of eGFP is exclusively observed during terminal erythroid differentiation. Expression of miR-144/451(eGFP) ignites immediately before the CFU-E stage and results in strong and complete labeling of all mature RBCs in circulation. Using competitive reconstitution experiments in the Ly5 transplant model, we show that eGFP linearly correlates with Ly5 expression. Thus, the miR-144/451(eGFP) allele represents a novel tool for the resolution of erythroid potential.