88 T. H. MORGAN AND ELETH CATTELL 



In the reciprocal cross eight large classes are expected, which 

 occur. No crossing-over was expected or rather could have 

 been observed even if it occurred: 



LWB 9 by LRN d" 



LWN (intermediate) 9 16 

 ^ LRN (intermediate) cf 15 



THE HEREDITY OF THREE CONTRASTED SEX-LINKED CHARACTERS 



In the following crosses three contrasted sex-linked factors are 

 involved, one for wings, one for eye color, and one for body color. 



The factors involved are the same as those of the preceding 

 crosses. Long wings (L) or normal wings contrast with minia- 

 ture wings (S), recessive to the former. Two factors, both sex- 

 linked, give, when both present, long wings, while miniature 

 wings are due to the absence of one of them; the absence of the 

 other producing the wing called rudimentary, but for simplicity 

 the letters L and S may be used, if one remembers that L is in 

 the X chromosome, and therefore present only in the female- 

 producing sperm; while S merely means the absence of L, and 

 alone stands for miniature wings. 



The factor for red eyes (R) is also sex-linked (in the sense that 

 the factor C is present); the absence of red is white eyes (W), 

 which means that the factor C is absent; small c would express 

 this condition more logically, but less graphically. 



The black factor B is also sex-linked, and present, therefore, 

 only in the female-producing sperm. Its absence is represented 

 by small b. The factor for yellow (Y) is not sex-linked, and, 



