Mendelism and evolution / by E.B. Ford.

  • Ford, E. B. (Edmund Briscoe), 1901-1988.
Date:
1931
Catalogue details

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

Credit: Mendelism and evolution / by E.B. Ford. Source: Wellcome Collection.

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    34 MENDELISM AND EVOLUTION extremities, the ears, muzzle and feet, which are subject to chilling, turn black ; for these parts are cooler than the rest of the body and this difference is sufficient totally to alter the effect of the Himalayan factor. That the darkening of this race is the result of tem¬ perature has been proved in the following way. If a patch of hair be shaved off the back of two Himalayan rabbits and the one be kept in a warm and the other in a very cold place, the hair which grows again will in the former environment be white and in the latter black (Schultz, 1920 ; Castle, 1924, pp. 218-19). 2. The Inteenal Environment It is seen, then, that the genetic factors interact with the environment to produce the characters for which they are responsible. But the environment is not only external but internal, and by the internal environment is implied the total effect of the genetic constitution of the animal. The means by which this can control the chain of reactions from a particular gene to a particular character, so as to produce phenotypic variability, must now be briefly sketched. The essential of Mendelian inheritance is its particu¬ late nature. This, of course, refers to the behaviour of the genes as individual units, it does not refer to the characters, for a single character is the result of the interaction of many genes. There are, in fact, unit factors but not unit characters in heredity. Factor interaction, then, is a matter of fundamental importance in the study of genetic action. Its recog¬ nition dates from the well-known observations of Bateson and Punnett (1905 ; and 1906, pp. 11-16) on comb shape in fowls. These authors found that the rose and pea combs were each dependent upon a
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