THE GENE 



3" 



tions of Baur, Correns, and Eyster we 

 see at once that all of them start from the 

 necessity, derived from the experiments, 

 of introducing some quantitative element 

 into the conception of the gene in order to 

 have a chance of sorting out such quanti- 

 ties. Baur prefers a definite quantity of 

 different unilocal genes, Correns accepts 

 a definite quantity of permutable side 

 chains, and Eyster believes in permutable 

 quantities of different genomeres. The 

 reader of the present writer's work will at 

 once realize how much these assumptions 

 may be simplified and brought in line with 

 all our other knowledge of the gene if the 

 unilocal genes, sidechains and genomeres 

 are replaced by molecules (or group of 

 molecules) of the substance called a gene. 

 If, as we believe we have proved, one of 

 the essential properties of the gene is its 

 quantity, the situation is the following: 

 The "pigmented" gene has a definite 

 quantity, say ten molecules. The muta- 

 tion to pigmentless consists in changing 

 this quantity into four molecules. Nor- 

 mal, stable genes have the elementary 

 property of being "adsorbed" in the 

 chromosome, always in their charac- 

 teristic quantity, at least in all cells up to 

 the point of their final determination. 

 Unstable genes, properly called by Correns 

 sick genes, lack something in their 

 - physico-chemical properties necessary for 

 constancy in their number of molecules. 

 In mitosis therefore the twenty molecules 

 present at the time of fission of the 

 chromosomes may be "adsorbed" by the 

 two daughter chromosomes say as 12. and 

 8. It is not necessary to work this out in 

 detail: The result must necessarily be the 

 same as in the other hypotheses. The 

 advantage is, besides the fitting into the 

 general theory of the gene, that no 

 different types of genes or genomeres with 

 quantitive assortment are needed but 

 simply the definite quantities of the 



one gene substance reckoned in numbers 

 of molecules (or molecule-compounds). 

 Thus the facts about unstable genes seem 

 to add new material to the already broad 

 basis of our general conclusions. 



G. THE NATURE OF THE GENE 



There are no direct facts giving informa- 

 tion about the nature of the gene. If our 

 conception is correct that the gene is a 

 definite quantity of something (of course 

 qualitatively different things in many 

 different genes) linked with a chain of 

 reactions with a velocity proportional 

 ceteris paribus to its quantity, it does not 

 single out a definite type of chemical 

 substance. However all general con- 

 siderations have led practically everybody 

 who discussed the problem since Driesch 

 in premendelian days and Hagedoorn 

 in early Mendelian days to regard the 

 gene as a type of enzyme and specifically 

 as an autocatalyst. The present writer 

 has also joined this view, the only alterna- 

 tive to which is at present agnosticism. 

 Of course this gives no information about 

 the members of the chain of reactions 

 catalysed by the gene. If Plunkett (19x6), 

 for example, concludes from his experi- 

 ments "that the gene acts as a true 

 catalyst" which as the first step in the 

 chain of reactions catalyses the production 

 of another catalyst, which in its turn is 

 connected with further reactions of definite 

 rate, this is not a different view from ours, 

 as Morgan ('z6) seems to believe, but a 

 specification of a more general assumption. 

 Further discussion of this point does not 

 seem profitable at present. 



H. THE INTERACTION OF GENES IN 

 DEVELOPMENT 



If we try to formulate definite ideas 

 regarding the gene and its mode of action 

 we do it with the end in view of under- 

 standing the role of the genes in directing 



