Figure 4: The effect of genome duplication and independent paralog loss on the evolution of lamprey-gnathostome conserved syntenic regions.

(a) Conserved synteny among the GnRH2, GnRH3 and (previously proposed) GnRH4 genes in lamprey, chicken and humans, including the medaka region for GnRH3, which is absent in tetrapods. The orientation of each chromosome (chr.) and scaffold (scf.) is indicated with line arrows. A pointed box represents the orientation of each gene. Open rectangles with red X's indicate lost GnRH loci. The presumptive ancestral state of the gene region is shown at the bottom. (b) Assembled lamprey Hox scaffolds and patterns of conserved synteny relative to human Hox clusters (human Hox clusters rather than chicken are used because all four human Hox syntenic regions are integrated into the human genome assembly). Three additional conserved syntenic genes, located adjacent to the PM2Hox cluster, are omitted owing to space limitations (retinoic acid receptor (RAR), heterogeneous nuclear ribonucleoprotein (HNRNP) and thyroid hormone receptor (THR)). Symbols indicate representative family members of lamprey-gnathostome homology groups.