1 is PHYSIOLOGICAL GENETICS 



mal development within t he sphere of influence of these read inns. 

 The more genes are involved in such dosage differences the larger 



this sphere of influence will be, and the more general the effect. 

 This conclusion, of course, is a direct consequence of the idea that 

 genes act together by controlling rates of reactions in develop- 

 ment, which have to be in proper tune in order to produce the 

 typical effect. The working of such a system to control develop- 

 ment was first conceived in a more generalized way (not related 

 to gene action) by Guyer (1911). It was later derived from 

 actual experiments in change of gene dosage on the basis of 

 Goldschmidt's discovery and analysis of the phenomenon for 

 which he coined the term inter sexuality (1912, 1915) and was later 

 elaborated as a general principle of physiological genetics (19206). 

 Bridges (1922) coined the term genie balance, which is frequently 

 used to describe these facts, though he did not think of minutely 

 interwoven reaction velocities but of an effect of different genes 

 pulling the phenotype in a plus or minus direction. This seems 

 too crude a way of describing the case. In using the term genie 

 balance, it must certainly be kept in mind that the balance, or, in 

 Goldschmidt's terminology, the quantitative relation or the tune, 

 is not one of the genes but of the gene-controlled reactions. 



In this way, the dosage relations mentioned above are supposed 

 to lead to a considerable upset of the balance of the gene-con- 

 trolled reactions concerned with development. It is in this 

 sense that facts of that type will lead to insight into the physiology 

 of genie action. It is not possible to recount all the phenotypic 

 effects caused by those compound changes in dosage. But there 

 are a number of facts that might furnish some information 

 toward our problems. 



There is first one set of facts in which the action of individual 

 genes is studied but where the quantitative steps have been 

 produced by addition of whole chromosomes or chromosome 

 sets. Here are a few examples to which ought to be added 

 innumerable cases in which the same mutant gene has been 

 compared in haploids, diploids, and tetraploids. 



Mangelsdorf and Fraps (1931) studied the vitamin content of 

 corn, which is higher in yellow than in white corn. As the 

 endosperm is known to be triploid, it is possible to build up 

 kernels containing the recessive genes for white in 0,1,2,3 doses 

 in the formulae (F = yellow, y = white) yyy, yyY, yYY, YYY. 



