It is now well established that before the teleost-tetrapod split, two rounds of large scale (often referred to as whole) genome duplication (WGD) occurred (2R), followed by a teleost-specific genome duplication event (3R) (Meyer and Van de Peer, 2005; Sharman and Holland, 1996; Sidow, 1996), greatly increasing the gene repertoire of the early vertebrates. Many of the genes that originated in the third (i.e. teleostean) genome duplication evidently have disappeared in the course of evolution, as the estimated total gene number in teleostean genomes does not greatly exceed the number of genes in other vertebrate genomes