Schematic view of the four categories of orthologous gene groups. (A) Gene groups with a 1:1 orthologous relationship between tetrapods and teleost fishes. (B) Gene groups that were duplicated specifically within the human or tetrapod lineage. (C) Gene groups that were duplicated through 3R-WGD. (D) Gene groups with no clear orthologous relationship between tetrapods and teleosts. Arrows denote gene duplication events. Triangles denote the orthologous gene clades derived from tetrapods, teleosts, or outgroup organisms (Ciona and Drosophila). Shaded triangles denote orthologous gene clades containing a human networks-related gene.