214 AN INTRODUCTION TO MODERN GENETICS 



these tetraploid gametophytes were made by regeneration. These 

 MMFF plants were also hermaphrodite, but even more protandric 

 than the MF diploid ones obtained in the first experiment, and the 

 female organs did not appear till the end of development. On the other 

 hand, MFF gametophytes, got by regenerating a sporophyte derived 

 from a cross between diploid FF and haploid iW, were protogynic, the 

 female organs appearing first. Similar diploid gametophytes, hetero- 

 zygous for the sex factors, have been obtained in other organisms, and 

 show other dominance relations. In Sphaerocarpus^ the female factor is 

 completely dominant, in Oedogonium^ partly dominant. The relations 

 between these hermaphrodites and zygophase intersexes is discussed 

 later (p. 232). 



The most interesting fact about gamophase sexuality is that it is not 

 restricted to a bipolar scheme as is zygophase sex. Particularly in 

 fungi, sporophytes are found which give rise to four types of gameto- 

 phytes which fall into two pairs within which copulation is possible.^ 

 The sporophyte can be represented as heterozygous for two factors, so 

 that it is AaBb. It gives the four haploid "sexes" AB, Ab, aB, ah, 

 which show no morphological differences but among which AB can 

 only conjugate with ah, and Ah with aB. This so-called multipolar 

 sexuality is further complicated by the occurrence of local races con- 

 taining different allelomorphs of the A and B loci, gametophytes 

 containing different allelomorphs being able to conjugate. 



It is perfectly clear that the multipolar sexuality in the gamophase is 

 something very unlike the bipolar zygophase sexuality which we 

 usually mean by the word sex. In fact, it has been suggested that it is 

 better to consider the A and B factors not as sex factors but either as 

 incompatibility factors, or, inversely, as factors positively leading to 

 conjugation. This is tacitly done even in those fungi which have only 

 two sexes, which are commonly referred to as + and — rather than 

 male and female. However, from the point of view urged later on in this 

 discussion, that sex is not the same thing genetically in different groups 

 of organisms, it becomes unnecessary to deny that name to the pheno- 

 mena in the fungi while allowing it to all the other phenomena which 

 concern the differentiation of the gametes. It might, however, be better 

 to consider the multipolar sexuality of Fungi as a gamete, rather than a 

 gamophase, sexuality. 



Some data have already been obtained on the physiological mechan- 



^ Allen 1932, Knapp 1936. 



2 Mainx 1933. ' Rev. Kniep 1928, 1929. 



