Evolution of the vertebrate neurotrophin and Trk receptor gene families

Studies of neurotrophins and Trk receptors in jawless fish have shed light on the course of events underlying the formation of these gene families. Th ey evolved early in vertebrate history during major gene duplication events , before the appearance of cartilaginous fish. The existence of multiple ge nes has permitted the diversification of neurotrophin and Trk receptor expr ession, and thereby enabling the acquisition of specific functions in selec tive neuronal populations.