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EDMUND B. WILSON 



be regarded as due to the absence of some particular constituent 

 that is present in the normal X-element. 



Fig. 8 Diagram of the distribution of the X- and Y-elements in successive 

 generations, illustrating sex-limited heredity. The underscored X-element (X) 

 is assumed to bear a factor for a recessive character (e.g., white eye-color), while 

 X represents the normal or dominant character (e.g., red eye-color). Y (being the 

 absence of X) likewise represents the recessive character. 



Upon pairing the affected male (XY) with the normal female 

 (XX) there are in the F, generation but two possible combina- 

 tions, XX and XY. The affected X-chromosome here passes 



