ABSTRACT
The history of the concept of the gene (Rheinberger et al, 2000) tells us that the gene was a theoretical concept before being conceived as an object or thing: the idea of the gene had appeared long before what would later be conceived of as its material support, the double-helical structure of DNA, had been discovered. After the work of Gregor Mendel on heredity (1863) had been rediscovered by Hugo de Vries, Carl Correns and Erich von Tschermak in the early years of the twentieth century, Wilhelm Johannson was the first to use the term gene in 1909, to name a holistically designed hereditary potential that was somehow secreted by the whole organism. In his view, genes were not to be considered as having a material nature, they were not to be considered as pieces of morphology, contrary to the suggestions made following the rediscovery of Gregor Mendel’s experimental work that there was something ‘particulate’ that was transmitted between generations. The gene, as Wilhelm Johannsen described it, ‘must be used as a kind of calculation unit. One does not have the right to define the gene as morphological unity in the sense of the Darwinian gemmules or of the biophores, or of other determinants or of other speculative morphological conceptions of that kind’ (Johannsen, 1909). Johannsen also insisted on the distinction between the phenotype (the observable characteristics of the organism1) and the genotype (containing the hereditary instructions). In his view, the phenotype and genotype, visible parts of the organism and hereditary instructions, were complementary realities interacting in the constitution of the living being, with no hierarchy of explanatory power (Barbieri, 2002). The identification of chromosomes as the cellular support of genetic information by Morgan, in 1913, revived the suggestion that genes were somehow material. Yet, the reification of the concept of gene did not reach its apogee until genes became defined as sequences of nucleotides localisable on chromosomes and the double-helical structure of the DNA molecule was discovered by James Watson and Francis Crick in 1952.2 Much of their findings were based on the work of others, and in particular, on the X-ray diffraction photographs produced by Rosalind Franklin
in 1951 at King’s College, London, which Watson and Crick acquired without Rosalind Franklin’s consent.3 Her X-ray photographs of DNA and her unpublished personal research notes were disclosed, without her knowledge and consent, by her colleague Maurice Wilkins to James Watson.4 Rosalind Franklin’s X-ray diffraction photographs were the first to show the essential structure of DNA: its double-helix shape which also indicated its method of replication. Although Franklin was the first to elucidate the basic helical structure of the DNA molecule, she never received due credit for her fundamental role.5
