7 



THE GENETIC SYSTEM AS A WHOLE 



Having examined the chief component parts of the 

 genetic system, we proceed to an examination of the way 

 it functions as a whole. This functioning and its conse- 

 quences constitute what is usually called Heredity. 



As we have seen, the genetic system consists mainly of 

 the chromosomes with their genes : the X-chromosomes, the 

 autosomes, and the Y-chromosome. 



Why are the other parts of the germ cells not to be 

 considered "materials of heredity" or parts of the genetic 

 system — the cytoplasm as well as the chromosomes? It is 

 known that the cytoplasm is of the very greatest importance 

 in the development of the individual and in the production 

 of its inherited characteristics. It is in the cytoplasm, 

 through interaction with the genes, that the differentiations 

 of the body arise. 



The role of the cytoplasm however differs from that of 

 the chromosomal materials in the following respects. Differ- 

 ent germ cells differ effectively in their genes, and it is to 

 these gene differences that the appearance of diverse char- 

 acteristics in different individuals is due. But as a rule there 

 is no evidence that the cytoplasm of different germ cells is 

 effectively diverse in such a way as to produce different 

 characteristics in different individuals. It Is therefore the 

 former — the chromosomes with their genes — that are com- 

 monly classified as the "materials of heredity," — more 

 properly perhaps the "materials of hereditary diversity." 



164 



