Schematic representation of the cellular composition of ineffective erythropoiesis in β-thalassemia. Most of the erythroid cells are proerythroblasts or basophilic erythroblasts, with an arrest of maturation in the polychromatic erythroblasts; many polychromatic and orthochromatic erythroblasts, exemplified here as cells with a fragmented nucleus, undergo apoptosis. This figure illustrates the notion that ineffective erythropoiesis is characterized by Epo-driven expansion of early-stage erythroid precursors, associated with apoptosis of late-stage erythroid precursors. Erythroid cells were reproduced from Servier Medical Art (smart.servier.com). Professional illustration by Somersault18:24.