Many transcripts show cell type-specific expression in hematopoietic subsets. (A) All blood cells derive from hematopoietic stem and progenitor cells (HSPCs) through common progenitors, including the common lymphoid and common myeloid progenitors (CLP, CMP). T and B-cells arise from CLPs, whereas red blood cell precursors (pRBCs) differentiate from CMPs. (B) Pairwise comparison of expression profiles from four cell types results in many differentially expressed transcripts but relatively few transcripts with cell type-specific expression. Total: the number of differentially expressed genes between two cell types. The numbers of cell type-specific genes are indicated below the panel.