Asxl1^tm1Bc/tm1Bc mutant mice have fewer committed myeloerythroid progenitors. In vitro colony formation of committed myeloerythroid progenitors (CFU-GEMM assay) is reduced in Asxl1^tm1Bc/tm1Bc mice compared with wild type in cultures of (A) E18.5 fetal liver (n = 2 wt, 3 mutant), (B) newborn spleen (n = 6 wt, 5 mutant), and (C) adult bone marrow (n = 9 wt, 6 mutant) *P < .05. ■ indicates wild type; □, Asxl1^tm1Bc/tm1Bc mutant.