Process of generating human and mouse exon orthologs. A. Flow chart of orthologous exon database building. B. Exons with N (N > 1) putative exon orthologs were further verified if these N exons belonged to the same united exon. C. Identification of fused and split exons through analysis procedure from putative orthologous exons. D. Confirmation of the correct orthologous exon pairs via anchor mapping for the rest of the putative orthologs yet to be verified.