78 



THE THEORY OF THE GENE 



notch dies. The factor is carried in the X-chromosome. 

 The notch female has one X carrvins: the factor for notch 

 and another X with its normal allelomorph (Fig. 45). 

 Half of her ripe eggs retain one X, half the other. If she 



Pig. 44. 



JMotch-wiDg, a dominant sex -linked, recessive lethal of Drosophila 



melanogaster. 



is fertilized by a normal male, an X-sperm uniting with 

 an egg carrying the normal X produces a normal daugh- 

 ter ; an X-sperm uniting with an egg carrying the notch- 

 bearing X produces a notch daughter. A Y-sperm uniting 

 with an egg carrying a normal X produces a normal son ; 

 a Y-sperm uniting with an egg carrying a notch-bearing 

 X forms a combination that dies. The output is two 

 daughters to one son. 



