The gene in search of an identity.

The concept of the difference between the potential for a trait and the trait proper, i.e., between the genotype and the phenotype, became clear only during the first decade of the century, mainly through the work of Johannsen. Although Johannsen insisted on that the terms he coined were only helpful devices to organize data about heredity, it is obvious that they were bound from the beginning to the hypothesis that there was "something" in the gametes that could be rendered to analysis as discrete units. These units were the genes. This reductionist yet materially non-committed attitude has been developed into what I called instrumental-reductionism: the genes were hypothetical constructs that were accepted "as if" they were real entities. The research program developed on such a concept was very successful, not least because this instrumental approach allowed maximum flexibility in the attachment of meaning of the genes. While most geneticists accepted one or another position of this flexible concept, others took more extreme positions. At the one extreme end of the conceptual continuum was the realist approach that argued that genes were discrete, measurable, material particles, and on the other end, the claim that the attempts to identify discrete units only led to hyperatomism of a holistic view appropriate to heredity. The acceptance of the gene as a material and discrete unit, in the beginning of 1950s, opened the way to a deeper level of conceptualizing both its structure ("cistron-recon-muton") and function ("one gene--one enzyme"). The discovery of the structure of DNA finally offered a chemical-physical explanation to the geneticist's requirements of a material gene. Thus, within less than 20 years the gene has been established as a "sharply limited segment of the linear structure" that is involved in the structure of a product or its regulation. However, with turning of much of the attention to the eucaryotic DNA, it was necessary to accommodate the gene to an increasing flood of findings that did not tally with its concept as a discrete material unit. Without much heart-seeking among geneticists, the gene regained its role as an instrumental unit, or even as just an intervening variable, "a quantity obtained by specified manipulation of the values of empirical variables".(ABSTRACT TRUNCATED AT 400 WORDS)