Sewall Wright, Sc.D. 



GENIC INTERACTION 



Genie interaction is a subject of great importance in two of the major branches of 

 genetics. It is obviously fundamental in physiologic genetics and is almost as funda- 

 mental in population genetics, including the genetic aspects of the theory of evolution. 

 I have been interested in genie interaction for both reasons and in about equal measure 

 since about 1915. In trying to keep up with both, it has sometimes seemed as if I 

 were trying to ride two wild horses bent on going in different directions. I shall try 

 to justify the attempt to keep them together. 



INTERACTION IN EARLY GENETIC RESEARCH 



The unit characters of the early geneticists probably seemed to most other bio- 

 logists merely another revival of the ancient doctrine of preformation, discredited by all 

 who, like Aristotle, Harvey, Wolff, and von Baer, had attempted to trace the step-by- 

 step elaboration of complexity in the process of development. The early geneticists 

 did relatively little to disavow this interpretation. They were too busy working out 

 the laws of transmission of these units and the patterns of organzation in the germ cells 

 to have much time for theoretical discussion. In pursuing this task, they were interested 

 in characters mainly as markers for genes. They were interested, for the most part, 

 only in good genes, consistently associated with easily classifiable characters. The 

 catchwords used for convenience in naming genes often seemed to others to imply that 

 geneticists thought of the organism as a mosaic of unit characters. 



The extent to which even the earliest Mendelians actually were preformationists 

 can easily be exaggerated. Interaction effects, such as those responsible for the familiar 



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