Origins of relaxin family genes in teleosts (bottom) and humans (top) determined by synteny map analyses. The ancestral Relaxin Family Loci (AncRFL) that are hypothesized to have been present in the common ancestor of teleosts and humans (tetrapods) are shown in the middle. We infer that AncRFLC duplicated giving rise to RFLCI (rln3) and RFLCII (insl3) prior to the divergence of teleosts and tetrapods. Names for the RFL proposed by Park et al. (2008) are given in brackets and underlined, those not used by Park et al., but inferred from this analyses are given in brackets with a dotted underline. The whole genome duplication (WGD) event resulted in two copies (paralogues) of each of the relaxin family genes in teleosts. AncRFLA gave rise to INSL5 and two paralogues in teleosts, insl5a and insl5b. AncRFLB was the predecessor of three human genes INSL4, INSL6 and RLN2, while the latter additionally underwent a recent duplication in primates producing RLN1. In teleosts, the RFLB gene, rln, is assumed to be orthologous to human RLN2. AncRFLC is hypothesized to have diverged into two loci: RFLCI harbouring RLN3 and the teleostean paralogues, rln3a and rln3b, and RFLCII, harbouring INSL3 and insl3. Duplicated copies of insl3 and rln in teleosts are believed to have been lost due to non-functionalization.