PASS Scripta Varia 21 - Pontifical Academy of Sciences

THE EVOLVING CONCEPT OF THE GENE
the ‘one gene-one enzyme’ hypothesis, supporting the view that genes carried
information related to the metabolic processes taking place inside the
cells and more specifically, that each individual gene is responsible for the
synthesis of a single enzyme. 17 Chemistry also had a role to play.Vernon Ingram
showed that changes in two abnormal hemoglobins due to mutations
were in each case confined to a single amino acid residue of the globin
polypeptide. Since there could be no doubt that genes determine the amino
acid residues of polypeptide chains, the expression ‘one gene-one enzyme’
was modified to ‘one gene-one polypeptide’. 18
The nature of the genetic material became even more tangible when Oswald
Avery 19 and collaborators showed that the substance causing transformation
in experiments that followed the protocols of Griffith’s was DNA.
Unambiguous confirmation of the DNA theory of inheritance was obtained
few years later by Alfred D. Hershey and Martha Chase. 20 The structure of
DNA proposed by Watson and Crick in 1953 gave the definite stroke to the
instrumentalist view of the gene in favor of the realistic one, initiating the
classical molecular gene concept. This states that a gene is a stretch of DNA that
encodes a functional product, a single polypeptide chain or RNA molecule.
Implicit in it is the idea that this genome unit performs one single function.
At last, then, structure and function were blended in the same concept.
The newly revealed structure of DNA also encouraged speculation
about the still prevailing idea of the gene as a unity of function, mutation
and recombination. Prior to 1955, several investigators had already obtained
the first hints that the unit of function might not be indivisible, since not
only more than one mutation could be mapped to the same gene but also
intragenic recombination had been detected in D. melanogaster and the fungus
Aspergillus nidulans 21 (see also references therein). Who most clearly confirmed
this was Seymour Benzer. The so-called cis-trans complementation
test led him to coin the word cistron to imply the unit of genetic function.
17
Beadle, G.W. and Tatum, E.L. Genetic control of biochemical reactions in Neurospora.
Proc. Natl. Acad. Sci. 27: 499-506, 1941.
18
Dunn, L.C. Old and New in Genetics. Bull. New York Acad. Med. 40(5): 325-333,
329, 1964.
19
Avery, O.T., MacLeod, C.M., and McCarty, M. Studies on the chemical nature of the
substance inducing transformation of pneumococcal types. J. Exp. Med. 79: 137-158, 1944.
20
Hershey, A.D., and Chase, M. Independent functions of viral protein and nucleic
acid in growth of bacteriophage. J. Gen. Physiol. 36, 39-56, 1952.
21
Portin, P. The origin, development and present status of the concept of the gene:
A short historical account of the discoveries. Current Genomics 1, 29-40, 2000.
The Scientific Legacy of the 20 th Century
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