3*6 



THE QUARTERLY REVIEW OF BIOLOGY 



necessary for normal development is 

 disturbed. It would be difficult to trans- 

 late this general statement into definite 

 terms without using the idea of definite 

 gene-quantities linked with definite rates 

 of reaction. 



A further method of studying genes in 

 different quantities is furnished by cases 

 of polyploidy, especially triploidy and 

 tetraploidy. Here the difficulties of clear 

 conclusions are still greater because all 

 genes are involved and the effect of one of 

 them in three or four quantities will be 

 completely outweighed and a normal 

 balance restored, since the whole system is 

 built up on the basis of such different 

 quantities. There is the additional effect 

 of the nuclear plasmic ratio, which in 

 these cases is a well known fact (see 

 Wettstein's review). Therefore conclu- 

 sions regarding our problem can hardly be 

 expected, with two exceptions, namely 

 when sex is involved in the triploid 

 intersexes where the presence of the X- 

 chromosome mechanism makes it possible 

 for sex genes to act in different quantities 

 which are not corrected by parallel 

 changes in the quantities of all the other 

 genes; and further when in triploid 

 hybrids the phenomenon of dominance is 

 involved. That triploid intersexuality 

 leads indeed to the same conclusions in 

 regard to the sex-genes and their action 

 as diploid intersexuality has been repeat- 

 edly shown by the present writer ('2.3, '2.5, 

 '2.7). The case of dominance will be 

 discussed later. 



C. EVIDENCE DERIVED PROM THE STUDY OF 

 THE EFFECTS OF EXTERNAL CONDITIONS UPON 

 THE PHENOTYPICAL EFFECT OF A GENE 



Thus far we have reviewed the evidence 

 furnished by the study of genes in different 

 quantities. Another method of attacking 

 the problem is the study of the action of 

 particular genes under different environ- 



ments. The first definite information 

 from experiments made with this end in 

 view, was found in the present writer's 

 experiments with intersexes. If the 

 results of his analysis of the phenomenon 

 of intersexuality are correct, namely that 

 intersexuality is produced if the two 

 simultaneous chains of reaction, those of 

 female and male differentiation, have a 

 point of intersection during development, I 

 it follows that intersexuality could be 

 produced within normal genie constitu- 

 tion, if such a point of intersection could , 

 be induced experimentally. The only 

 visible method for such an experiment was 

 the use of low temperatures, on the : 

 supposition that the sex-differentiating! 

 reactions and the other reactions con-i 

 trolling rate of development might have 

 a different temperature coefficient. Such} 

 experiments were performed many times,; 

 always with positive result, ('2.1). As. 

 a matter of fact Kosminsky (09) hadi 

 already performed the same experiment, 

 with the same result without knowledge 

 of intersexuality and all the questions 

 discussed here, and has since enlarged his 

 former results (^4). One further conse-: 

 quence (which Prof. J. Huxley kindly 

 suggested) is that similar experiments per- 

 formed with intersexual stock must shift: 

 the degree of intersexuality towards higher: 

 intersexuality. This experiment was also 1 

 performed successfully. 



These experiments led to a very impor- 

 tant conclusion : The effects of temperature 

 (or other experimental conditions) may 

 be phenotypically identical with the 

 effect of a different gene, the reason being 

 that in both cases the rate of a definite 

 reaction is changed, in the same sense. 

 This consideration furnished a simple 

 explanation for ('zob) such phenomena 

 as e.g. the phenotypic identity of heritable 

 geographic forms with forms produced in 

 temperature experiments on butterflies 



