Figure 9. Hypothesis regarding evolution of the cyp19a1 gene in the Actinopterygian lineage (ray-finned fish).

From an ancestral gene having brain and gonad functions, the teleost specific genome duplication gave birth to two copies that evolved differently in Elopomorphs (Eels) and other teleosts. Soon after the duplication, eels probably lost one copy of the cyp19a1 gene and this remaining copy retained brain and gonad functions. In other teleost fishes, a sufunctionalization process occurred that led to partition of functions between the two copies, cyp19a1a (gonad) and cyp19a1b (brain).