SEX AND GENES 



203 



explanation is obvious, if the X-chromosomes carry the 

 differential genes involved, namely, the red- and white- 

 producing genes. The son gets his single X from his 

 white-eyed mother ; and the daughter gets also such an X, 

 but also one from her red-eyed father. The latter being 

 dominant, the daughter has red eyes. 



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Fig. 116. 

 a, The reduced group of chromosomes in man, according to de 

 Winiwarter; b, chromosome group in man, according to Painter; 

 c and d, side view of first maturation division showing the separa- 

 tion of the X- and Y-chromosomes, according to Painter. 



If these two individuals are inbred there will appear 

 in the next generation white-eyed and red-eyed offspring 

 in the ratio of 1 : 1 : 1 : 1. This ratio is due to the distribu- 

 tion of the X-chromosomes, as shown in the middle of the 

 diagram (Fig. 115). 



In passing, it is not without interest to note that the 

 cytological evidence and the genetic evidence, especially 



