is a key regulator of the early development of the vertebrate forebrain and sensory organs. In this study, we describe for the first time three paralogues in lamprey, representative of one of two basally diverged lineages of vertebrates-the agnathans. We also first describe three genes in sterlet-representative of one of the evolutionarily ancient clades of gnathostomes. According to the analysis of local genomic synteny, three genes of agnathans and gnathostomes have a common origin as a result of two rounds of genomic duplications in the early evolution of vertebrates. At the same time, it is difficult to reliably establish pairwise orthology between genes of agnathans and gnathostomes based on the analysis of phylogeny and local genomic synteny, as well as our studies of the spatiotemporal expression of genes in the river lamprey and the sterlet . Thus, the appearance of three paralogues in agnathans and gnathostomes could have occurred either as a result of two rounds of duplication of the vertebrate common ancestor genome (2R hypothesis) or as a result of the first common round followed by subsequent independent polyploidizations in two evolutionary lineages (1R hypothesis).