Different Types of Sex Determination 469 



become females only by the combined action of phi and I, will pro- 

 duce with males from arrhenogene mothers an arrhenogene offspring, 

 since these males have the same constitution as the second type of 

 females except for the absence of phi. But this complicated system still 

 does not suffice to explain amphogenic offspring of monogenic mothers. 

 The proposed explanation is that the penetrance of I is less than 100 

 per cent, and in the absence of penetrance the other realizators again 

 act alone. Even this does not suffice: in addition a monogenic line 

 must have a weak F and a strong M complex and, in order to explain 

 all details, still other assumptions have to be made. 



There is no need to enlarge on the utter artificiality of this "poly- 

 factorial theory" of sex determination, which in the end must go back 

 to the F/M balance plus all kinds of modifying actions. I have no 

 doubt that Vandel's explanation covers the facts in principle, though 

 some modifying actions will have to be explained in terms of plasmon, 

 predetermination, and modifiers. But this is nothing unusual, and is 

 within the facts known for both the sex determination via a 2X-1X 

 mechanism and for many other known genetic actions. It would, in 

 addition, be very odd to assume that nature had invented (i.e., built 

 up by selection or fortuitous drift) such an unmanageable, unreliable, 

 and queer system of producing sexual dimorphism when the simple 

 mechanism of F/M balance through the 2X-1X mechanism is available. 

 Such considerations will excuse me from reporting and analyzing other 

 cases which have been claimed for — to be frank — the monstrosity of 

 so-called polyfactorial sex determination. This must, of course, not be 

 confused with the already discussed problem of whether F and M are 

 single loci or linked groups of such or what else. Even the AG idea — 

 the sex-promoting genes — which we discarded above, is a completely 

 different problem. 



C. SEX IN HAPLOIDS 



We have discussed thus far only the theory of sex determination 

 in diploid organisms, and have found that no types could be estab- 

 lished different from the standard type of F/M balance, regulated by 

 the 2X-1X mechanism, including its variants and, from case to case, 

 special modifier actions. The same is also true for the haploid lower 

 plants or the haplophase of others, as I tried to show a long time ago 

 (1929a). The work of the Hartmann school (see 1943), especially, has 

 established that the same genetic setup as in diploids is at work in 

 principle. The difference in detail between the explanations based 

 upon Correns' scheme, used by Hartmann, and my point of view is 



