LINKAGE OF THE FACTOR FOR BIFID WING. l6l 



EXPERIMENT IX. 



For this experiment both males and females with crossed over 

 factors were used. These were taken from the F 2 generation 

 produced in Experiment VIII. On looking over Table XV. it 

 will be noticed that the F 2 BfR females possess the gametic 

 constitution of BfRX-BfWX. Both of the combinations BfR 

 and BfW have been produced in the normal percentage by a 

 crossing over in the F 1 generation of factors originally coupled in 

 the grandparents. 



The F 2 LW males have been similarly produced, their factors 

 L and W being crossovers. 



All combinations, therefore, introduced into the F 1 generation 

 have been produced by a rearrangement of the original combina- 

 tions owing to crossing over. 



Table XVII. shows the expected results of such a crossing. 



TABLE XVII. 



To ILLUSTRATE EXPERIMENT X. (CROSSOVERS.) 



P 1 BlRX - Bl'WX = BfR 9 L\VX - o = LWcf 



Gametes BfRX, BfWX LWX, o 



F 1 BfRX - LWX = LR9 BfRX - o = BfRc? 



BfWX - LWX = L\V9 BfWX - o = BfWcT 



LR of F 1 X BfW of F 1 



( (i) BfRX, (2) LWX, I BfWX, o 



FlEggS 1(3) BfWX, ( 4 )LRX Sperm i 



F 2 BfRX - BfWX = BfR 9 BfRX - o = BfRcT 



LWX -- BfW'X == LW9 LWX - o = LWcf 



BfWX -- BfWX == BtAV9 BfWX - o = BfWcf 



LRX - BfWX = LR 9 LRX - o = LRd" 



In spite of the conditions of the experiment the combinations 

 introduced into the F 1 generation persist with a strength of 

 linkage approximately equal to that existing among the original 

 combinations. 



Table XVIII. gives the actual results of the experiment. 



