PHENOMENA OF INHERITANCE 



279 



with a white-eyed male half of the females of 

 F 2 are red-eyed and half are white-eyed, and 

 half of the males are red-eyed and half are 

 white-eyed. 



If now one of these white-eyed females is 

 bred with a red-eyed male all the females of 

 the Fi generation are red-eyed and all the 

 males white-eyed ("criss-cross" inheritance) 



Flies 



Chromosomes 



xc 



6 



Parents 



I x' I ! Gametes 



X K 9 



2x: 



Fi 



Gametes 



X 



xi m x© m fz 



? ' 9 c? 6 



Fig. 60. Reciprocal cross of Fig. 61. Parents, white-eyed 

 2 and red-eyed <£; F l5 red-eyed J and white-eyed £ ("criss- 

 cross inheritance"); F 2 , equal numbers of red-eyed J and $ 

 and white-eyed J and <^. The distribution of the sex chromo- 

 somes is shown on the right, as in Fig. 59. (After Morgan.) 



