Conserved synteny around the PDE1C locus (loci) in tetrapods and teleost fishes. Triangles indicate gene loci and their direction of transcription. Doubly conserved synteny, which was derived from the teleost-specific genome duplication [18, 19], is indicated by yellow shading and labeled "CS (conserved synteny)-1" and "CS-2." Orthologous/paralogous relationships among PDE1C genes are shown by solid magenta lines. The dashed lines indicate putative orthologous relationships predicted in the Ensembl genome database . The solid yellow and green lines show phylogenetic relationships of neighboring "unknown" genes around stickleback PDE1Cb loci, which are estimated in the present study [see Additional file 1, Figure S1]. The PDE1Cx (Ensembl ID: ENSGACP00000001336) [see Additional file 1, Table S1] of the stickleback is located alone in a small contig (Scaffold 809; 12 kbp), and therefore has no synteny information.