Ancient genomic linkage for FGF and Sprouty genes. a Gene loci maps for human FGF and Sprouty show linkage in the human genome. FGF1/2 (FGF-A class) genes are linked to Sprouty orthologs in the human (a) and mouse genomes (data not shown; Itoh and Ornitz 2004). Members of FGF-B (FGF3), FGF-C (FGF4 and FGF6) and FGF-G (FGF19 and FGF23) classes also show linkage in mammalian genomes. The approximate distances separating linked genes in kilobases (kb) is shown below each linkage group. b In the FGF-D class, three of four genes (NvFGF8A, 204532, and NvFGF8B) are all linked in the Nematostella genome, with NvFGF8A also closely linked to the Sprouty ortholog, NvSprouty, suggesting that this association between FGF and Sprouty genes is an ancient one, predating the cnidarian–bilaterian split (∼600 MYA). There is also evidence of linkage between other FGF genes in Nematostella, with two pairs of FGFs closely associated on two different genomic scaffolds