One model for movement of globin genes during the evolution of jawed vertebrates. Top, gene clusters in contemporary species; bottom, inferred gene arrangements in the last common ancestor to jawed vertebrates; middle, some of the possible gene movements mapped onto an evolutionary tree (thick gray lines). Genes are indicated by boxes, with those above the line transcribed from left to right and those below the line from the right; red, β-like globin genes; yellow, α-like globin genes; light blue, OR genes; other colors, other genes; small orange circles, major regulatory regions. All the known genes encoding hemoglobins expressed in erythroid cells are shown, as well as other genes that are most consistently diagnostic for the loci. Numbers to the left of each cluster specify the chromosome on which it is located; for the frog gene clusters, the scaffold number (preceded by s) is given. The Greek letter name is specified for hemoglobin genes in human, platypus and chicken, but generic 'α-globin' or 'β-globin' is used for frog and fish because the genes are less well characterized. In the X. tropicalis genome assembly (version 4.1), scaffolds 733 and 357 are not connected. Maps of the gene clusters were derived from a combination of the assembled genomes and recent publications [2,4,15]. The gene maps are not complete or to scale; see [2,4] or the genome assemblies for more complete information.