212 Cytoplasm as Seat of Genetic Properties 



genes requires a definite cytoplasm in order to succeed fully or at 

 all. Though the idea behind the term is derived from unequivocal 

 facts, I think that this theory might lead to confusion if it were 

 misunderstood to mean that there are different kinds of "genes," 

 some dependent or partly dependent and others not dependent upon 

 the specific features of the cytoplasm. 



We shall meet again with the same logical situation and the 

 danger that genie actions, varying under different conditions, or 

 in different systems, or as a consequence of a qualitatively different 

 kind of action, will be mistaken for differences in the nature of the 

 "gene" which suggest characterizing types of genes. (See chapter 

 on dosage.) In the interest of clear notions on "cytoplasmic heredity," 

 I prefer to look at the facts in terms of genically controlled processes, 

 all of which take place in the cytoplasm as substratum and are 

 therefore dependent upon its biophysical and biochemical nature. If 

 it is a fact that these substrate conditions are different in taxonomi- 

 cally different forms (in the widest sense of the term), the full and 

 normal performance of these genically controlled processes (re- 

 action chains) is possible, within a foreign cytoplasm, only when its 

 substrate activity lies within the threshold limits of the gene-substrate 

 interaction in question. Thus the cytoplasmic maternal effect is the 

 combined result of the threshold conditions of the individual or 

 combined genically controlled processes, and the amount of bio- 

 chemical difference of the foreign cytoplasm which shifts those re- 

 actions within or beyond the thresholds. The biochemical cytoplasmic 

 difference, being probably in the nature of a basic, quantitative 

 property like the various levels of the oxidation-reduction system, 

 affects the actions of the entire genome, and it is only the quantity 

 (visibility and localization) of the effect that changes with threshold 

 conditions for individual traits. Oehlkers (1952a), in his review of 

 cytoplasmic heredity, draws basically similar conclusions when he 

 says that the alleged plasmon-sensitivity of some genes is relative. 

 "As a matter of fact there is no special 'sensitivity' of the genes but 

 only a special reaction among other possibilities of reaction, which 

 alone is conspicuous because it falls outside the normal ... in prin- 

 ciple all genes are plasmasensitive because we may connect all with 

 some specific collaboration with the plasmon." 



A few experimental or theoretical attacks have been made on 

 the problem of what these cytoplasmic conditions are. We considered 

 them to be of a rather simple generalized type affecting threshold 

 conditions for genically controlled reactions with a substrate. Schlos- 



