CHAPTER 6 



SEX-DETERMINATION IN FISH AND 



THE LOWER ALGAE 



SEX IN PARAMECIUM AND FUNGI 



SEX-DETERMINATION IN BRYOPHYTES 



SEX IN THE HIGHER PLANTS 



Fish. The identification of the sex-chromosomes in fishes is 

 difficult, but the evidence derived from genetic experi- 

 mentation with Lebistes, Aplocheilus and Platypoecilus 

 has shown that in some species the male is the hetero- 

 gametic sex and that in others he is homogametic. 



Winge (1922, 1934) has produced convincing evidence 

 that in Lebistes reticulatus there are several mutant genes in 

 the Y-chromosome. Spot, a large black spot on the dorsal 

 fin, is a character exhibited by a certain geographical 

 variety of this fish. Spot (^ x 5 of a variety lacking this 

 spot=F.i and F.2 spot males. Non-spot (^ x 5 of a spot 

 variety=F.i and F.2 non-spot males. The character of the 

 father is transmitted to all his male descendants. Winge 

 explained this by postulating that the male was XY and 

 that the spot gene was Y borne. 



Since then Winge has described eight other characters 

 that in inheritance behaved like spot. He has also described 

 eight other recessive characters, patterns of male coloration, 

 the genes for which are presumably resident in the X for the 

 characters were not exhibited by the F. i but reappeared in 

 50 per cent, of the males in F.2. Occasionally, however, an 

 F.I male exhibited the character. Winge explained this by 

 postulating that the X was homologous to a portion of the Y 

 and that crossing-over had occurred between these homo- 

 logous parts. When such an exceptional F.i male was used 

 in breeding, all his sons displayed the character. 



In two varieties Winge observed a marked inherited 

 tendency toward the production of females with male-like 

 gonopodia and remarkable in that in them the heterozygous 



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