Evolution.

Society for Experimental Biology

Date:: 1953

Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Evolution. Source: Wellcome Collection.

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444 POSTSCRIPT a species. But from an evolutionary point of view it would be advisable to consider the possibility, within the time scale of evolution, of the flow of genetical material in manners such as those set out in Fig. i. To return again to the possibility of chemical evolution of genes: we can get a clearer picture of the possible significance of this if we consider two of the possible methods of function of a gene in controlling the production of an enzyme. One method is that a polypeptide is adsorbed upon a gene, and becomes folded into a unique pattern which enables the polypeptide Genes of other species Genes of symbionts and parasites, etc. 1 Chromosome genes Plasmagenes Viruses Fig. I. to function as an enzyme or apoenzyme. Another totally different hypo¬ thesis is that a gene controls an ' assembly line ' responsible for the synthesis of a polypeptide unique in its amino-acid sequence. Or perhaps both mechanisms are involved. In either case, it is obvious that a change in chemical composition of a gene, if carried beyond a certain limit, will result in a change in the pattern of folding, or amino-acid sequence, of the poly¬ peptide. Changes in chemical composition of a gene may depend upon other than suddenly procured mutagenic events, and may proceed gradually by gradual changes in composition. The occurrence of such changes may not result in any change in, for example, gene-controlled enzyme, until the quantitative chemical changes in the gene affect its behaviour qualita¬ tively, when a sudden change in gene action will appear and simulate