Selection of the Genetic Basis for an Acquired Character

Abstract

IT is a very well-known fact, referred to in nearly all text-books of genetics, that the expression of many genes is influenced by the genetic background in which they find themselves, and that by selection and inbreeding in a uniform environment one can build up lines which differ in the frequency or intensity of manifestation of the mutant character. That Dr. Begg has shown that this is true of ‘antennaless’ does not seem to provide any very close parallel with the facts reported in my letter¹. His thesis amounts to the suggestion that one is entitled to argue that, provided selection is effective in respect of any particular character, it must be effective in respect of all, since all characters are to some extent dependent on the genotype. This somewhat abstract truism was, of course, one of the lines of thought which led me to perform the experiments recorded in my letter, and prevents one being surprised at the demonstration that it is possible to select successfully for the capacity to respond to an abnormal environment; but an a priori justification is not quite as informative as the experiment itself, since it cannot tell one how effective the selection will be. Further, neither Dr. Begg's argument nor his experiment leads to the conclusion that, after several generations of selection in the abnormal environment, the character will continue to be developed by animals cultured under normal conditions; and this was the essential point.