Evolution of the vertebrate vitellogenin cluster. (a) The vertebrate vitellogenin cluster was generated by two ancestral gene duplications (1 and 2). (b) The phylogeny of vertebrate Vtgs should reconstruct the ancestral gene duplications correctly (left), but observed phylogenies (right, merged and deduced from [1, 7, 8, 10]) indicate multiple, independent duplications (black circles) of Vtg2/3. Gene names are as used in the literature. A unifying nomenclature is shown to the right of the expected phylogeny. The remaining functional platypus VtgX gene is most likely a Vtg2 [9, 10].