Molecular biology was born when geneticists, no longer satisfied with a quasi-abstract view of the role of genes, focused on the problem of the nature of genes and their mechanism of action’’ (Morange1998). 1940s, Avery and his colleagues showed that DNA is the hereditary material of bacterial by demonstrating that the causative agent in bacterial transformation, which entailed a heritable change in the morphology of the bacterial cells was DNA (Avery et al. 1944) and also experiment proof that convinced the scientific community was the experiment of Hershey and Chase (1952), in which these authors showed that the DNA is gene material of bacteriophages. Togather these two experiments show that gene is DNA molecule which are heridetory material of bacteria and virus. In 1953 structure genetic material had been analyzed by Watson and Crick (1953), and Crick had stated the ‘Central Dogma’ of molecular biology and its related ‘sequence hypothesis’ (1958): colineareity of DNA sequence –mRNA sequence –Protien sequence. Dounce (1952) and Gamow (1954) independently presented the so-called colinearity hypothesis, according to which the linear structure of DNA determines the linear primary structure of a polypeptide.
The new, molecular concept of the gene was the result of technical developments that allowed much more detailed maps of the chromosome (‘fine structure mapping’) and the interpretation of the results of this enhanced form of genetic analysis in the light of the new understanding of the material gene. The experiments of Benzer (1955, 1957, 1959, 1961) involving the genetic ®ne structure of the bacteriophage T4 rII-region turned out to be of fundamental importance. With the aid of a selective technique, he was able to map hundreds of mutations of that region into a linear order. The gene as the unit of function was not indivisible; within the gene, independently mutating mutation sites existed, which could be separated from one another by means of genetic recombination. Benzer created a new terminology. Seymour Benzer, for example, used this system in an entirely “classical” manner to increase the resolving power of genetic mapping techniques down to distances of a few nucleotide pairs, thus preparing the ground for Francis Cricks sequence hypothesis. Interestingly, Benzer came to the conclusion that “gene” was a “dirty word,” as the inferred molecular dimensions of the gene as a unit of function, recombination, and mutation clearly differed. Consequently, he suggested referring to genetic elements as cistrons, recons and mutons respectively (Holmes 2006). Finally, by studying the A-protein of the tryptophan synthethase Yanofsky'sgroup was able to show that the material counterpart of both recon and mutonwas one single nucleotide pair in the structure of DNA (Crawford & Yanofsky,1958; Yanofsky & Crawford, 1959). Thus, the cornerstone of the neoclassical view of the gene became the one cistron/one polypeptide hypothesis, which replaced the old one gene/one enzyme hypothesis.
To summarize, the neoclassical concept of the gene, as outlined above, can be summarized in the formulation “one gene—one mRNA— one polypeptide,” which combines the idea of mRNA, as developed by Jacob and Monod (1961a); Gros et al. (1961); Brenner et al. (1961), and the earlier “one gene—one enzyme” hypothesis of Beadle and Tatum (1941). Another version of this hypothesis is that of “one cistron—one polypeptide” (Crick 1963), which emerged as a slogan in the 1960s–1980s. Altogether, the conceptual journey from Johannsen’s totally abstract entities termed “genes” to a defined, molecular idea of what a gene is, and how it works, had taken a little over half a century (as reviewed in Portin and Adam, 2017)
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