  Weber identifies six different gene concepts, beginning with Darwin's pangene concept (1868) and ending with the contemporary concept of molecular genetics. He distinguishes the contemporary molecular concept from the classical (or ‘neoclassical’) one on the basis of how geneticists described their functional role (RNA/protein coding versus general function unit), their material basis (RNA/DNA versus chromosome), and their structure (discontinuous linear -- with introns and exons versus continuous linear) as well as on the basis of the criteria experimentalists used to identify genes (by gene product versus complementation test). 