The word “gene” wasn't coined until early within the 20th century, by the Danish botanist Johannsen (1909), but it rapidly became fundamental to the then new science of genetics, and eventually to all or any of biology. . within the beginning, the concept was used as a mere abstraction. Indeed, Johannsen thought of the gene as some sort of calculating element (a point to which we'll return), but deliberately avoided speculating about its physical attributes (Johannsen 1909). By the second decade of the 20th century, however, variety of genes had been localized to specific positions on specific chromosomes, and could, at least, be treated, if not thought of precisely, as dimensionless points on chromosomes. Furthermore, groups of genes that showed a point of coinheritance might be placed in “linkage groups,” which were the epistemic equivalent of the cytological chromosome. We are called  “classical period” of genetics. By the first 1940s certain genes had been shown to possess internal structure, and to be dissectable by genetic recombination; thus, the gene, at now , had conceptually acquired one dimension, length. Twenty years later, by the first 1960s, the gene had achieved what appeared like a definitive physical identity as a discrete sequence on a DNA molecule that encodes a polypeptide chain. At now , the gene had a visualizable three-dimensional structure as a specific quite molecule. we'll call this period—from roughly the top of the 1930s to the first 1960s—the “neoclassical period.”  

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