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Concurrent evolution of the claudin family and the vertebrate body plan. The number of distinct claudin genes found to date in each clade is given in brackets. The appearance of those vertebrate characters that we found to be associated with claudin expression is indicated beside the stem lineage (13). Arrows indicate two presumptive genome duplications (16); a third genome duplication may have taken place in ray-finned fishes alone (15, 47).
