Functional classification of blood cell types. (a) Maximum-parsimony phylogenetic reconstruction of the hematopoietic lineage using pathprints calculated from (a) human  and (b) mouse  gene expression experiments. (c) Combined human-mouse tree based on shared informative pathways that resolve trees (a) and (b) and the pathway heat-map. The myeloid (yellow) and lymphoid (purple) branches are indicated, and dark branches represent agreement with the canonical lineage. See Additional file 10 for pathway annotations.