224 THE THEORY OF THE GENE 



chromosomes, and that crossing-over between these chro- 

 mosomes may take place. 



For example, the character, white body color, is sex- 

 linked in inheritance. Its allelomorph is red body color. 

 When a pure white female was mated to a pure red male, 

 the sons and daughters (FJ were all red. When these 

 were inbred they gave, 



Eed 5 Red $ White 5 White $ 

 41 76 43 



Assuming that the genes for white are carried in the two 

 X-chromosomes of the female and designating such a 

 chromosome by X^ (Fig. 129), and assuming that the 



white Q bij red o 



qerm cells 



Fi 



Fig. 129, 

 Diagram showing the inheritance of a character whose gene is 

 carried by the ' ' Y-chromosome, ' ' as well as by the X-chromosome. 



gene for red is carried both by the X and the Y of the 

 male, and designating these by X^ and Y^, the cross given 

 above works out on the XX-XY formula as shown in Fig. 

 129. If red (r) dominates white (w), both sons and daugh- 



