Genome datasets used to define the evolutional classifications. The evolutional classifications defined in our analyses are indicated, together with arrows covering the range of their putative evolutional origin (e.g. Vertebrate genes represent the genes that are considered to have already existed before vertebrate evolution). Numbers in parentheses indicate developmental genes and total genes classified in each evolutional classification. These classifications are consistent with a recent report [25, 26] that most of the duplications of developmental genes occurred before bilaterian and vertebrate evolution, supporting the appropriateness of our homologue determination (See Additional file 1: Taxonomic classification of homologues of mouse protein-coding genes according to taxonomic range.). See also Methods for the definition of evolutional classifications and "developmental genes".