Génetica

Current Genomics, 2000, 1, 29-40

29

The Origin, Development and Present Status of the Concept of the Gene: A Short Historical Account of the Discoveries
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Petter Portin*
Laboratory of Genetics, Department of Biology, University of Turku, FIN-20014 Turku, Finland Abstract: The classical view of the gene prevailing during the 1910’s and 1930’s comprehended the gene as the indivisibleunit of genetic transmission, genetic recombination, gene mutation and gene function. The discovery of intragenic recombination in the early 1940’s led to the neoclassical concept of the gene, which prevailed until the 1970’s. In this view the gene or cistron, as it was now called, was divided into its constituent parts, the mutons and recons materially identified as nucleotides. Each cistron wasbelieved to be responsible for the synthesis of one single mRNA and concurrently for one single polypeptide. The discoveries of DNA technology, beginning in the early 1970’s, have led to the second revolution in the concept of the gene in which none of the classical or neoclassical criteria for the definition of the gene hold strictly true. These are the discoveries concerning gene repetition andoverlapping, movable genes, complex promoters, multiple polyadenylation sites, polyprotein genes, editing of the primary transcript and gene nesting. Thus, despite the fact that our comprehension of the structure and organization of the genetic material has greatly increased, we are left with a rather abstract, open and general concept of the gene.

The gene is operationally defined on the basis offour genetic phenomena: genetic transmission, genetic recombination, gene mutation, and gene function. These criteria of definition are interdependent; we cannot for example observe gene function or gene mutation without transmission, while on the other hand, we cannot observe transmission without gene function. According to the so called classical view of the gene, which prevailed during the1910's and 1930's, all four criteria led to one and the same unit. According to the classical view, the gene was the smallest indivisible unit of transmission, recombination, mutation and gene function. The classical view of the gene begins with the work of Gregor Mendel [1], in which he explained definitively the transmission of genes -or elements as he called these units of inheritance - and theirindependent assortment. The gene as the unit of transmission means that each gamete includes one

unit of each gene. The term "gene" was coined by Wilhelm Johannsen [2]. He wished this unit of heredity to be free of any hypotheses regarding its physical or chemical nature; i.e. the genes could be treated as calculating units. The actual formulation of the classical concept of the gene must beattributed to the American Thomas Hunt Morgan and his school, which included Calvin Blackman Bridges, Herman Joseph Muller and Alfred Henry Sturtevant. They created the chromosome theory of inheritance, according to which the genes reside in the chromosomes like beads on a string. The chromosome theory of inheritance begins, however, already in the works of Walter S. Sutton and Theodore Boveri in1903 [3, 4]. They called attention to the fact that the Mendelian rules of inheritance were explained by the behaviour of chromosomes in meiosis. Already earlier Boveri [5] had demonstrated the individuality of chromosomes, and in 1904 [6] he showed that chromosomes preserved their individuality during cell division. Both these characteristics of chromosomes are naturally necessary properties of thehereditary material. The chromosome theory of inheritance developed as a precise theory due to the work of the Morgan school. They observed [7, 8] that the number of linkage groups in Drosophila
© 2000 Bentham Science Publishers Ltd.

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This work was supported by The Academy of Finland.

* Address correspondence to this author at the Laboratory of Genetics, Department of Biology,...