M. R. IRWIN 



Universify of Wisconsin 



Chapter 15 



Specificity 

 of Gene Effects 



If an attempt were made to survey all the possible ramifications suggested 

 by the title of this paper, it should include much of the published work in 

 genetics. It is of course a truism to all students of genetics to state that some 

 sort of differential specificity towards the end product must exist between 

 allelic genes or their effects could not be studied. It would be very interesting 

 as a part of this discussion to attempt to trace the change in concepts held by 

 various workers during these past fifty years concerning the nature and paths 

 of action of the gene. However, beyond a few remarks, such considerations 

 are hardly within the scope of this chapter. 



Since the effects of genes can be recognized only if there are differences in 

 the end product, it is quite natural that the differences in the experimental 

 material first subjected to genetic analyses should have been those which 

 were visible, as differences in form, color, etc. Although the pendulum has 

 swung somewhat away from intensive investigations of such hereditary char- 

 acteristics, it should be emphasized that by their use the underlying mecha- 

 nisms of heredity have been elucidated. 



Major attention was given by most of the investigators during the first 

 quarter of this century to the effects of respective genes upon individual 

 hereditary characters. In some quarters there was an oversimplification in 

 the interpretation of the relation of the gene to the character affected by it. 

 Gradually, however, the concept has become clearer that the majority of 

 hereditary characters — even many of those which had previously appeared 

 to be most simply inherited — are affected by many genes. 



An early observation of gene specificity, too long neglected by all but a few 

 geneticists, was that made by Garrod in 1909 (see 1923 edition of Inborn 



* Paper No. 433 from the Department of Genetics, University of Wisconsin. 



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