/ffO 



PHYSIOLOGIC GENETICS 



modifications of the 9 : 3 : 3 : 1 F 2 ratio (9 : 3 : 4, 9 : 7, etc.) , were recognized very early 61 • 232 

 and interpreted as due to epigenetic chains of reactions. 



ELEMENTARY GENIC ACTION 



It is generally accepted now that the physiologic action of genes is wholly by 

 imposition of specific patterns on macromolecules 1450 and even this is thought to be by 

 steps (DNA-RNA-polypeptide, etc.). The classes of characters that have seemed most 



Fig. 2 1 . Diagram of relations of genome and external environment to observed 



CHARACTERS AT VARIOUS LEVELS OF ORGANIZATION. 



Behavior 



External 

 Environment 



Histogenesis 



Extraorqanic 

 Structure 



Homeostasis vs. Disease 



Organic 

 Structure. 



Cell 

 Constitution 



Morphogenesis 



Genome 



Gene Duplication 



/ 



Cell 

 Product 



Metabolism 



Genome 



favorable for study of the first links in the control of characters have thus been antigenic 

 and enzymatic specificities and the more elementary metabolic processes. 



One of the most significant results from immunogenetics has been the usual 

 occurrence of a one-factor relation between any particular antigenic reaction and a 

 particular gene (or group of alleles) irrespective of the situation at other loci. Even so, 

 the demonstration of hybrid substances by Irwin shows that there may be interactions 

 among loci even at this level. 641 



Another significant result is the occurrence of a very large number of alleles at 

 many of the loci with antigenic effects. While attempts at subdivision of the loci 

 according to the pattern of responses to multiple test sera have been demonstrated 



