  The most rigorous formulation of the unconnectability objection can be found in the early writings of Rosenberg who once contended that there is an unbridgeable conceptual gap between the classical and molecular theories of genetics (1985, 1994). In support of this contention, Rosenberg argued that relations between the gene concept of classical genetics and the concepts of molecular genetics are hopelessly complicated “many-many” relations that will forever frustrate any attempt to systematically connect the two theories. Rosenberg began his analysis by pointing out that in classical genetics, genes are identified by way of their phenotypic effects. Classical geneticists identified the gene for purple eye-color, for example, by carrying out carefully orchestrated breeding experiments and following the distribution of eye-color phenotypes in successive generations of a laboratory population. The reason classical genetics will never be reduced to a molecular-level science, according to Rosenberg (1985), is that there is no manageable connection between the concept of a Mendelian phenotype and that of a molecular gene: