1 78 T. H. MORGAN AND CLARA J. LYNCH. 



explained by strong linkage of the yellow factor and the factor for 

 wings. The Mendelian expectation (unmodified by linkage and 

 viability) is three long Grays to one long Black (3 : i). There 

 are actually 1,858 long gray flies to 916 long black, or a ratio of 2 to I. 

 This is the linkage ratio when two strongly or completely linked 

 factors are concerned. 



Since the males and females count equally in the result it is 

 not necessary to separate them. We are indebted to Mr. A. H. 

 Sturtevant for the following F 2 count derived from the same FI 

 material as the last. We are also indebted to him for being first 

 in pointing out the interpretation of this result. 



Winged Gray. Winged Black. Wingless Gray. Wingless Black. 



458 230 185 o 



There are 458 winged Grays to 230 winged Blacks, or almost 

 exactly 2:1. 



In the following analysis Y = yellow factor; y its absence; 

 B = black factor (sex-linked), and b its absence. The formula 

 for the female gray fly is YBXYBX, and for the male, YBXYb. 

 The formula for the female black fly is yBXyBX, and for the male 

 is yBXyb. 



The evidence indicates that the wingless condition differs from 

 the winged condition by a loss. Large W may then stand for 

 that ' factor " in the original complex that has been lost. In 

 this sense large W means in this case Wings (here long) ; and 

 small w stands for this loss and in the formula represents the 

 wingless condition, which is of course the result of the interaction 

 of all the remaining wing factors. 



wYBX wYBX Wingless gray 9. 

 WyBXWyb Winged black a*. 

 FI wYBX WyBX Winged gray 9. 



wYBX Wyb Winged gray cf . 



Gametes of wYBXWyBX Eggs. 



FI WyBXw YBXWybw Yb Sperm. 



wYBX WyBX Winged gray 9 . 

 wYBX wYBX Wingless gray 9 . 

 WyBX WyBX Winged black 9 . 

 WyBX wYBX Winged gray 9 . 



