(a) Synteny for chromosomal regions containing the GPR15-C10ORF99 pair. The pair and their neighbouring genes in vertebrate genome fragments are shown. Deep red shading represents exon 1 of the CDHR1 gene of amniotes. Deep grey color represents exon 1 of the CDHR1 gene of amphibians and fishes. Light red represents exon 1 of the C10ORF99 gene. 3'rd WGD indicated the fishes that underwent a third round of whole-genome duplication. 