Cumulative validation of bidirectional promoters in the cow genome. A set of confirmed bidirectional promoters from the human RefSeq annotations (Hg18 assembly) was mapped to orthologous positions in the cow genome. If the cow transcript data independently identified a bidirectional promoter at that same location (with ≤ 1,000 bp intergenic distance) these predictions were considered validated (purple bars). Otherwise the predictions were classified as low stringency (i.e., > 1,000 bp). The validation data are additive, accumulating information from the top to bottom of the image (i.e., from RefSeq, high stringency data to EST, high stringency data, respectively). Dark blue and and medium blue bars designate promoters that lack annotation for one or both of the two genes in the pair, respectively. Light blue bars designate gene pairs lacking an ortholog of either gene in the pair.