Evolution of the gonadotropin-releasing hormone (GnRH) gene family in relation to vertebrate tetraploidizations

► The GnRH gene family consists of three paralogs in gnathostomes, GnRH1, 2 and 3. ► The three genes arose by two rounds of tetraploidization in the ancestral vertebrate. ► The GnRH3 gene has likely been lost early in the tetrapod lineage. ► A putative GnRH4 was probably present at the origin of vertebrates and may still exist in some extant species.