472 Genetics of Sex Determination 



Nevertheless, Hartmann derives from it the mechanism in the 

 haploids. According to him, there are no autosomal sex determiners 

 (reahzators) but only both A and G genes distributed all over the 

 autosomes in equilibrium (but when the facts make this equilibrium 

 improbable, he has no hesitation in assuming that there are more G 

 than A genes). The sex chromosome of the haploid contains the 

 "realizator" either F or M, haploids with F being females, or + forms, 

 with M being males, or — forms. The diploid phase will be hermaph- 

 roditic. But now the female haploid may show male characteristics and 

 vice versa. Since only one realizator is present, the relative number or 

 activity of A or G genes must be variable. Then relative sexuality is 

 found which now requires different valencies of F and M but without 

 a F/M balance. 



Apart from the a priori improbability of this scheme (on which 

 different minds may have different opinions), we must ask whether 

 the existing facts permit a decision. Most of the facts and variants 

 found in Hartmann's book and discovered since may be formally 

 explained in both ways, with more or less additional assumptions. But 

 there are a few facts which may be considered decisive and are also 

 recognized as such by Hartmann. The decisive experiments in favor of 

 my view have been made by Knapp (1936) and Knapp and Hofmann 

 ( 1939 ) . By X-raying of spores and vegetation points of female thalli 

 of Sphaerocarpus, a certain number of male gametophytes were 

 obtained. According to Hartmann's theory, the chromosomes should 

 be 7A + IX, and the X should contain only the female determiner F 

 (realizator). Knapp proved in an excellent genetic and cytological 

 analysis that the X rays had knocked out a piece of the X-chromosome 

 and that maleness resulted even when a small piece was removed, and 

 the number of male plants increased with increase in the size of the 

 deficiency. This deficiency must have contained the F factor or factors, 

 and therefore the M in the autosomes took over. It should be added 

 that these mosses (Allen, 1917) have a visible XY group of chromo- 

 somes. 



A still more powerful proof for the correctness of my conclusions 

 is the following (discovered by Bizet, 1952). In the mold Podospora 

 the haploid plant can be made diploid by so-called heterokarya 

 (union of two plants) or by homokarya (diploidization of the same 

 plant). In the latter, if Hartmann were right, the homokaryon should 

 be of one or the other sex containing only FF or MM. Actually, the 

 homokarya are hermaphrodites producing both sex organs. This is 

 possible only if my interpretation of the genetic constitution is cor- 



