Different Types of Sex Determination 473 



rect. It is important that the mating type is either — or + , as expected 

 in a homokaryon, if mating type is independent of the F/M mecha- 

 nism. We do not intend to discuss here the latter problem, which is 

 one of physiology of fertilization and self-sterility. However, I may 

 point out again that the inclusion of this problem in that of genetic 

 sex determination by Hartmann and his school has led to much ob- 

 scuring of the genuine genetics of sex and will necessitate one day a 

 critical analysis and an unraveling of the separate problems. But let 

 us return to the localization of F and M in haploids. 



In favor of Hartmann's hypothesis are the claims that the assumed 

 F and M realizators in the sex chromosome of female and male hap- 

 loids are located at different loci and can be brought into one chromo- 

 some by crossing over, with the result of a hermaphrodite FM. This 

 would be a proof if the other hypothesis led to a different expectation, 

 which it does, as MF + F should not be a hermaphrodite but a hyper- 

 female. But Moewus says (see III 5 C a aa) that with F and M in 

 one chromosome, the haploid is a hermaphrodite. If we could accept 

 this as proved, Hartmann would be right in assuming a different 

 sex-determining mechanism for at least this haploid organism. Un- 

 fortunately, the crossover experiments of Moewus have evoked much 

 criticism, and, for the time being, I am not inclined to base such a 

 far-reaching decision upon them. Recently the Hartmann school itself 

 repeated Moewus' experiments, and in a suflBciently large sample no 

 such crossovers could be found (Forster and Wiese, 1954a). A few 

 other such examples have been claimed. Among them is a case (see 

 Hartmann, p. 142) in which both haplonts, one with FM in one 

 chromosome and the other without any "realizators," developed into 

 monoecious plants. This makes me very skeptical in regard to the 

 explanation as well as the experiments, though markers of the chromo- 

 somes were involved here. The crossing over is clearly not proved but 

 is assumed on the basis of the general theory. Thus, on the whole, I 

 do not think that it has been proved that haplonts have a radically 

 different mechanism of sex determination from that of diplonts. 



D. THE HYMENOPTERA TYPE 



This leads to what is probably the most complicated situation. 

 In a number of animals, especially all the Hymenoptera, males are 

 developed from haploid parthenogenetic eggs. Females may be pro- 

 duced from fertilized eggs, but also sometimes from parthenogenetic 

 ones, and thus are always diploid. In special cases, males may be 

 derived from fertilized eggs. There is an immense variation in detail in 



