Cross-species mapping of mouse bidirectional promoters. (A) The 1,105 protein-coding gene pairs are represented as 2,210 individual genes. These genes were mapped to the human genome to identify the presence of orthologous bidirectional promoters. If the human annotations independently supported a bidirectional promoter at the orthologous location, and the genes on each side of the human promoter were shown to be orthologs of the mouse gene pair, then promoter orthology was confirmed. The annotations in the human included the human Known Genes (hg38_KG) where no more than 1,000 bp separated the transcription start sites in human as well as in mouse. Results using an unlimited distance between the genes in human are shown in the panel hg38_KG_NoLimit. A composite dataset of the human Known Genes and human ESTs occupies the lower panel, hg38_KG_spEST. (B) The 732 gene pairs represented by 1,464 individual genes in the mouse spliced ESTs were mapped to the mouse genome to identify the orthologous bidirectional promoters. The three panels use the same validation approach as in panel A, shown by the same labels.