III. THE CYTOPLASM AND THE ACTIVATION OF THE 



GENE 



In our discussion of the facts and interpretations of physiologi- 

 cal genetics, we were concerned mainly with the action of the 

 genes, situated within the chromosomes of the nucleus. We 

 took for granted that the seat of the reactions controlled by 

 the genes is the cytoplasm, both the cytoplasm of the individual 

 cells and the cytoplasm of a group of cells taken together as a 

 unity (a field or territory in the sense of experimental embry- 

 ology). The role of cytoplasmic differentiation in development 

 and determination has been discussed in connection with the 

 phenomena of stratification, primary chemodifferentiation, and 

 different types of induction. In all these cases, the cytoplasm 

 was considered to be the substratum upon which the genes 

 work, though the processes happening within the cytoplasm may 

 take their independent course once started by the action of the 

 genes. In this chapter, we have to consider the facts that may 

 lead to a better understanding of the part assigned to the cyto- 

 plasm in heredity. 



The questions that will have to be answered are: 



1. If the cytoplasm is the substratum upon which the genes are 

 acting, is it possible to formulate more specific ideas of this 

 interaction? 



2. At the outset of such an interaction, which must be of an 

 orderly sequence, a process is supposed to occur that may be 

 called the activation of the gene. What does this mean? 



3. Is the activity of the cytoplasm in conditioning orderly 

 development always steered by the genes, or is an independent 

 activity of the cytoplasm known? 



4. If the cytoplasm has independent genetic properties, are 

 these of the same type as the properties controlled by genie action, 

 or are they of a different, possibly more generalized, type? 



1. INTERACTION OF NUCLEUS AND CYTOPLASM 



The first question, regarding the type of interaction of genes 

 and cytoplasm, is difficult to answer, because only very indirect 



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