DIFFERENT TYPES 



OF SEX DETERMINATION 



A. SO-CALLED PHENOTYPIC SEX DETERMINATION 



In the work of Hartmann (see 1943) and his students, the term 

 "phenotypic sex determination" plays a considerable role. The idea is 

 that internal or external environment alone decides whether a female 

 or a male is formed. However, this deciding action is supposed to 

 work upon the complicated genetic setup which Hartmann assumes 

 under the influence of Correns. An animal or plant with phenotypic 

 sex determination is supposed to have all the female and male deter- 

 miners A and G and, in addition, the female and male realizators or 

 trigger genes MMFF, these in equal potencies so that none of them 

 controls sex. The environment determines the suppression of either 

 A or G, with the result that either females or males are produced. In 

 other words, we need a complicated genetic mechanism of sex deter- 

 mination, which, however, cannot function unless the environment 

 gives one of the component genetic entities a lift. I prefer to say that 

 the norm of reaction of the genetic determiners is such that they pro- 

 duce their effect only in a definite environment, which is nothing but 

 an application of the classic definition of genie action. The term 

 "phenotypic sex determination" is thus not only unnecessary but 

 completely confusing. It is still more so when we realize that the true 

 sex determiners F/M are completely balanced but that the A and G 

 factors alone are affected by the environment. I showed above that 

 the A and G factors are a complicated assumption completely unwar- 

 ranted by the facts. Thus we have the old story of an equally bal- 

 anced F/M action in the absence of the 2X-1X mechanism, and a 

 norm of reaction for the action of F and M that allows a shift in the 

 amount of their activity which can be brought about by factors of the 

 environment. This is, as far as the effect is concerned, the same as 

 such a shift by the presence of specific modifiers, or by a change of 

 potency of F and M, or by the interaction with different plasmons, 

 examples of all of which we have discussed. We have ( 1 ) genetic sex 

 determination without a 2X-1X mechanism to shift the balance; (2) 

 a norm of reaction of F and M which is more than usually sensitive to 

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