THE NATURE OF THE GENE 285 



A. Mutation as Change in Quantity 



This interpretation of gone mutation has been derived by 

 Goldsehmidt (since 1916) from the following facts and delibera- 

 tions: 



1. There is a basic difference of action between one and two 

 sex-determining genes, showing that the dosage of the gene is 

 important for its action. 



2. Intermediate conditions are found, showing that an orderly- 

 series of effects exists between the action of one and two sex genes 

 (intersexuality). In this case, these actions may be described in 

 terms of intermediate quantities (between 1 and 2) of sex genes. 

 This enables one to predict the results of any possible combina- 

 tion or addition of different sex genes, results that were consist- 

 ently obtained. For this reason, it could be concluded that the 

 different potencies of sex genes, varying between the potencies 

 of one or two actual doses, were dosage differences themselves. 



3. It was shown that the different quantitative combinations 

 of sex genes acted by controlling developmental reactions of 

 definite velocity, which were proportional to the assumed relative 

 quantities of the sex genes. The simplest assumption that one 

 can make regarding the action of an active substance, ceteris 

 paribus, is that it follows the mass laws in which one variable 

 is the quantity (concentration) of the catalyst. The assumption 

 that this is the meaning of different gene quantities would there- 

 fore link the action of the gene to elementary facts of chemical 

 kinetics. 



4. It was found that many cases exist in which the effect of 

 actually different gene doses is roughly proportional to the dose. 



5. It was found that series of conditions of genes exist, the 

 multiple allelomorphs, in which frequently the effects are pro- 

 portional to a simple seriation of the genes in question. The 

 differences of these alleles may be called their potencies; if com- 

 pared with the other facts, they may be considered actual dosage 

 differences. 



6. It was found that in the cases mentioned under 5, the effect 

 in heterozygotes and compounds frequently appeared to be con- 

 sistently equal to the added effects of the respective simplex genes. 



From such facts, many details of which have been reported 

 above, Goldsehmidt concluded that the majority of mutations 



