Survey Sequencing and Comparative Analysis of the Elephant Shark (Callorhinchus milii) Genome
Figure 5
The Evolution of Vertebrate Hox Cluster Organization and the History of Whole-Genome Duplications in Vertebrates
The additional Hox genes in the lamprey (shown as white arrows) are the result of a lineage-specific duplication of the “AB” or “CD” Hox cluster. In the horn shark, only a partial HoxD cluster (from HoxD5 to HoxD14) has been sequenced, and HoxB and HoxC clusters are yet to be sequenced. The number of Hox clusters in various lineages is consistent with one round of genome duplication (“1R”) during the evolution of jawless vertebrates from chordate invertebrates, a second round (“2R”) before the emergence of jawed vertebrates but after the divergence of the lamprey lineage, and a third round (“3R”) in the ray-finned fish lineage before the divergence of zebrafish and fugu lineages. See text for the source of Hox cluster information.