FISH 47 



characters with genes in the X showed up faintly. He inter- 

 bred these varieties and obtained a small proportion of XX 

 individuals (according to the genetical evidence) that were 

 males in appearance, behaviour and function. 



When these XX males were mated all of their progeny 

 turned out to be females. The father mated to his daughters 

 gave none but females. Mated to some of these new 

 daughters he produced a completely male individual among 

 the progeny. When this new male was mated with his sisters 

 about half of the offspring were males. 



In this way Winge produced a new kind of male, XX 

 instead of XY. The X was no longer the sex-diiferential and 

 the characters based on X-borne genes were exhibited by 

 both sexes, behaving as characters based on autosomal- 

 borne genes. The new fish was XX male; XY female; but 

 the sex- differential function had been assumed by an auto- 

 some through the accumulation in it of male-determining 

 genes. 



It now became possible for Winge to produce YY sons 

 who inherited the Y-borne characters from both father and 

 mother. 



Winge concludes that male-determining and female- 

 determining genes are scattered throughout the autosomes 

 and sex-chromosomes alike and that sex-determination is 

 the outcome of the specific balance betw^een the two 

 kinds. 



Aida (192 1, 1930, 1936), working with the Japanese 

 Killifish Aplocheilus latipes, obtained results completely 

 parallel with those of Winge and offered a similar inter- 

 pretation. 



The genetical evidence relating to the Mexican Killifish 

 Platypoecilus maculatus and obtained by Bellamy (1928) 

 pointed directly to the conclusion that in this species, in 

 contrast to Lebistes, the female is the heterogametic sex 

 and that crossing-over occurred between the X and the Y. 

 In two broods Chavin and Gordon (1951) obtained none 

 but males. The female parents were XX, the male YY, so 

 that all the offspring were XY, which is characteristic of the 

 normal male in this strain. 



