308 



THE QUARTERLY REVIEW OF BIOLOGY 



the present writer; we may, therefore, 

 begin with an evaluation of his primary 

 facts and conclusions, which will be 

 followed by a critical review of the 

 different types of further evidence on the 

 same point. These sections (A, B) will 

 be followed by a review of the other 

 methods of attack upon our problem and 

 their results as we see them (C-F). 

 Two short general sections (G, H) will 

 conclude the paper. 



A. THE EFFECTS OF THE SAME GENE IN 

 DIFFERENT QUANTITIES 



I. The genes of sexual differentiation 



In a series of papers from 191 1 to 19x7 

 the present writer analyzed the case of 

 experimental intersexuality in the gipsy- 

 moth, which furnished him the first 

 notions about the action of a gene. 

 Neither the experiments nor the conclu- 

 sions will be reviewed here in detail (A 

 rather complete review up to 19x6 is 

 found in Goldschmidt, y 2.f); only that 

 part will be mentioned which is decisive 

 for the present problem: viz. the proofs 

 for our claim that in these experiments 

 really different quantities of a gene were 

 studied and further that these different 

 quantities were linked up with typical 

 effects. 



One of the fundamental results of this 

 work was the experimental proof that in 

 dioecious animals both sexes contain 

 the determiners or genes for the production 

 of either sex and that the actual sex is 

 determined by a quantitative relation or 

 balance between these two sets of genes. 

 As one of them (M in the Abraxas type, 

 i 7 in the Drosophila type) was shown to 

 be situated in the X-chromosome and 

 therefore present in one or two quantities, 

 the other (F in the Abraxas type and M in 

 the Drosophila type) being outside of the 

 X-chromosome and always present in the 



same quantity, it became clear that 



the mechanism of the sex-chromosomes 



furnishes a method of associating the same 



dose of the one sexual determiner with 



either one or two doses of the other. As 



the two doses of the determiner within 



the sex chromosomes produce the sex of 



their own type (male — Abraxas, female — 



Drosophila), but with one dose present 



sex follows the determiners outside of the 



sex-chromosomes, the sexual decision is 



brought about by the relative quantities 



of the two types of genes according 



M 

 to the formula F ^ MM (Abraxas) and 



-FF 



M ^ cc (Drosophila). This conclusion, 



which was inevitable from the writer's \ 

 experiments, has since been corroborated 

 by all the new evidence. Here then was 

 the possibility of studying the effects of 1 

 one gene in different quantities, other 1 

 things remaining equal. We speak here ; 

 of one gene F or M. Leaving aside : 

 certain autosomal modifiers which we : 

 found (and which were later similarly 

 found by Bridges in Drosophila), we cannot 

 prove experimentally that F and M are 

 single genes. But all our large experi- 

 mental evidence shows that they are 

 inherited like single genes. For our 

 conclusions it is then irrelevant whether 

 the symbols F and M are the equivalents 

 of single genes or of an unknown group of 

 inseparable genes. If it is proven that 

 the formulae in question are the true 

 representation of the case — and this is 

 proven — it follows that the quantity of 

 each of these genes plays an important 

 role in the action of the gene: a quantita- 

 tive relation or balance has no meaning 

 except in connection with the absolute 

 quantities back of the proportion. 



The full proof for these conclusions was 

 derived from the experiments, in which 

 forms were crossed which are distin- 



