Ts65Dn spleens harbor increased hematopoietic progenitors. Colony-forming assays were performed using nucleated bone marrow cells or splenocytes isolated from Ts65Dn mice and euploid littermate controls. indicate euploid controls; indicate Ts65Dn. BFU-E indicates erythroid burst-forming unit; CFU-GM, granulocyte-macrophage colony-forming unit; and CFU-MK, megakaryocyte colony-forming unit. n = 3 Ts65Dn; n = 3 euploid littermates. Differences in spleen colony number are P = .1 for CFU-MKs, P = .24 for CFU-GMs, and P = .6 for BFU-Es. Error bars represent SE.