242 Cytoplasm as Seat of Genetic Properties 



part of nuclear genie material. This is bound to lead to hypotheses in 

 many fields which, then, will be based not on established facts but 

 on a suggestive and misleading terminology. Therefore I should like 

 the term "plasmagene" to disappear from the genetic vocabulary. 

 Sonneborn himself says, only two pages after the quotation: "... a 

 priori considerations render improbable the possibility that such 

 plasmagenes could persist and multiply except in cytoplasm of a 

 definite constitution, which could scarcely be free from decisive gene 

 modification. I therefore doubt whether totally gene-independent cyto- 

 plasmic inheritance exists in any form, based on plasmagenes or 

 otherwise." 



One might discuss the problem of whether viruses, kappa 

 particles, mitochondria, genoids, and cytoplasmic genetic material are 

 a series of external aspects of the same basic thing, afid thus lead to a 

 comparison with the nuclear genetic material resulting in the con- 

 clusion that all of them are "genes." I am convinced that this is a 

 speculation not based upon the facts, either those relating to the 

 so-called gene, or those relating to viruses, or those concerning cyto- 

 plasmic inheritance including the plastids. For the time being it 

 appears safer to be noncommittal and to look at the entities involved, 

 genes in the classic or modern sense, a generalized plasmon, mito- 

 chondria, plastids, virus-like parasites, or symbionts and genuine virus 

 as diflFerent organizations with different physiological activities. 

 Ephrussi (1953) has proposed treating the kappa particles at least as 

 a kind of model for cytoplasmic particulate inheritance. I do not agree 

 with this compromise because it can serve only to put another prop 

 under the tumbling plasmagene. Why not simply let it drop out? 



My point of view, of course, does not exclude the formulation of 

 ideas on the relative values, merits, and even phylogenetic origin of 

 all these entities. A most penetrating analysis of the whole situation, 

 drawing mainly upon facts of bacterial and yeast genetics, has been 

 made by Lederberg ( 1952 ) . He considers as one of the decisive points 

 involved a clear notion of what genetic autonomy or self-reproduction 

 is. Therefore he asks what criteria are applicable when deciding 

 whether small units in the cell are self-reproducing or rather re- 

 produced by the organism as a whole. "The problem is usually 

 approached by abstracting the unit in question from the organism. 

 If it is then no longer produced by the organism, it is concluded to be 

 self-reproducing. This has unfortunately been taken to mean that the 

 unit is autosynthetic, but the proof shows only self-dependence, not 

 self-suflBciency. In this context, self-dependence describes a wide 



