196 



T. H. MORGAN. 



Black long 9, 

 Gray vestigial 



bV g bV g . 

 Bv g Bv g . 



cf or 9 , 



Gametes of FI 



bVgBvgbVg Eggs 

 Sperm. 



F 2 



-B F ff 6 F ff , gray long, B V g Bv g , gray long. 

 bV g bV g , black long, bV a Bv , gray long. 

 Bv g b V g , gray long, 

 fo> s bV g , black long, 



Bv a Bv g , gray vestigial. 

 bv g Bv g , gray vestigial. 



The expectation is 4 gray long, 2 black long, 2 gray vestigial, 

 o black vestigial. The data show that the gray vestigial run 

 behind expectation, which is due to viability (crowding out 

 through competition). It is evident that the expectation would 

 be the same if the failure to cross over occurred in the female 

 instead of in the male as here assumed. In order to test which 

 sex failed to give crossing over the following matings were made. 

 (i) Black, long winged females were mated to gray, vestigial 

 winged males. The FI flies c? and 9 were gray, long. The FI 

 males were bred to black vestigial females and gave two classes. 



If we assume that there has been no crossing over in the FI 

 heterozygous males the result is explicable, as shown in the 

 following analysis, except in so far as the gray vestigials are 

 crowded out. 



Black vestigial 9 , 



bv g bv 



g , 



bv g bVg, black long, 

 bv g Bv g , gray vestigial. 



