Fig. 4. Structure and evolution of hox clusters.

a, Schematic illustration of the sterlet hox complement. We identified 88 hox genes plus one pseudogenized hoxd14 gene (indicated by psi). All hox clusters are retained in duplicate. b, Reconstruction of the ancestral actinopterygian condition and the inference of gene losses across the gnathostome phylogeny on the basis of the sterlet pretetraploidization hox complement in combination with that of the gar. The inferred ancestral Hox complements are shown in purple (likewise indicated by the purple arrowhead in the tree) for gnathostomes, in blue for Sarcopterygii and in orange for Actinopterygii.