Tprx loci are not present in rodent genomes. In the human genome, the Tprx family contains one probable functional gene (TPRX1) and a possibly non-functional tandem duplicate (TPRX2P) at chromosome 19q13, either side of the Otx-family CRX gene. The additional Tprx loci, TPRX1P1, TPRX1P2 and TPRXL, are elsewhere in the genome and are not shown. Examination of the region syntenic to human 19q13 in other mammals reveals clear orthologues of Tprx family loci in cow and dog, but not mouse and rat. In rodents, another homeobox gene Crxos1 is found. Orange arrows indicate homeobox genes; grey arrows are non-homeobox genes.