Genie Control of Development 363 



continuous character from the continuous base. Therefore, here pene- 

 trance and expressivity are correlated; further, they are rather sensitive 

 to environment, sex, right-left differences, and single strong enhancers. 

 The conclusion is drawn that multiple factors are genes whose remote 

 effects only are studied. Direct gene effects are considered to be 

 highly specific and acting through difi^erent physiological channels (a 

 conclusion shared by Haldane, 1954, in a qualitative biochemical 

 sense). Secondary and tertiary genetic effects are not specific; all or 

 most genes influence ultimately, in progressively indirect ways, many 

 different processes. Gene effects will tend to be additive, if they 

 affect the same process in a similar way, that is, if they are unspecific. 

 Such remote gene effects will tend to be additive also with various 

 major genes with which they enter into modifier relationships. Thus, 

 quantitative inheritance here looks very different from Mather's poly- 

 genic systems, if the problem is looked at from the point of view of 

 genie action. 



b. Dominance, potency, penetrance 



Dominance is one of the basic facts of genetics, the complete 

 understanding of which should shed light upon the problem of genie 

 action. Therefore an analysis of dominance has been tried repeatedly. 

 It is generally accepted as a fact that dominance or recessivity is not 

 a property of a mutant locus, but a result of the action of the mutant 

 locus in relation to the entire system of reactions constituting develop- 

 ment. This is clear at the outset because dominance may often be 

 shifted by external agencies, for example, temperature and the inter- 

 ference of other loci, acting as dominance modifiers; both agents are 

 known to shift genie effects by a change in the genically controlled 

 processes and not by affecting the genie material itself. It has been 

 held that dominance of the wild type over most mutant loci is con- 

 trolled by a modifier system which has been selected in order to keep 

 the heterozygote on the adaptive level of the homozygote. Whether 

 this is true or not does not affect the present discussion, because domi- 

 nance modification by modifiers must be understood also in terms of 

 genie action upon some feature of the reaction chains constituting 

 development. If we could find out how dominance modifiers inter- 

 fere with the specific chains of reaction in development, we could 

 draw conclusions concerning the mode of genie actions, which should 

 be the same as those reached from a study of dominance without 

 modifiers. 



We may visualize the meaning of the dominant, not dominant, or 



