396 Action of the Genetic Material 



pleiotiopy." This probably represents the only genuine pleiotropy, 

 namely, one and the same genie action affecting completely different 

 processes. Both Griineberg (1952a) and Caspari (1952) doubt whether 

 such a genuine pleiotropy actually exists, and I agree with this. But 

 I think that the nearest approximation to it, interference pleiotropy, 

 is frequent. We mean by this that a genetically controlled process 

 interferes with other independently determined actions, with the re- 

 sult that they are shifted in a way they could also be shifted directly 

 by independent mutation. The mutant aa may have a pleiotropic 

 action which is based upon a single difference of primary action from 

 that of AA, of any type of mutant action known. The actions of the 

 normal loci BB, CC, DD may require a definite condition at a 

 definite time (model: a definite pH) in order to run properly. If aa 

 affects this condition in the wrong way, the B, C, D reactions may be 

 thrown out of gear; that is, they may run off exactly as if B, C, D 

 had mutated. The result is a change of mutational order in all the end 

 products of B, C, D which looks like (and indirectly is) a pleiotropic 

 action of aa. I think that this type of pleiotropy is present whenever 

 completely unrelated and unrelatable effects are found: for example, 

 in Drosophila the effects of Dichaete on wing posture and bristles, of 

 silver on pigmentation, shape of wings, and a pigment-suppressor 

 action. The correctness of the interpretation is borne out by the fact 

 that these different pleiotropic effects may be affected individually in 

 special conditions. I have already mentioned (I 3 C ee ccc) my finding 

 that in silver the suppressor action could be separated from the others; 

 for vestigial we found a temperature effect upon the dominance of 

 the pleiotropic bristle effect alone ( Goldschmidt, 19S5a,b); other 

 examples could easily be found. To this probably belong the cases of 

 extreme pleiotropic action described by Timofeeff (1931) and Neel 

 (1942a). 



This leads to another group of facts concerning pleiotropy which 

 contains information on the interplay of genie actions. In a system of 

 the type just assumed for what is actually genuine pleiotropy, it is to 

 be expected that, generally, environmental agents as well as the 

 internal environment (modifier systems) will affect pleiotropic traits 

 differently. Many such facts are known, especially from Drosophila 

 literature, and it is hardly necessary to go into details, some of which 

 are found in Caspari's review. But we may return to a related subject 

 (discussed briefly in III 5 C fo), the behavior of pleiotropic traits in 

 multiple allelic series. (For more details see Stern, 1930; Goldschmidt, 

 1938a; Caspari, 1952.) In most multiple allelic series it is possible to 



