1916] Reeves: Inheritance of Extra Bristles in Drosophila 511 



Thus selection seems to have no influence on the inheritance of 

 an increased number of extra bristles in this strain. Six-bristled flies 

 occurred in crosses with normals and extras, and even in crosses of 

 two normals. 



Selection did not increase the number of extras appearing in high- 

 grade families, namely in families resulting from crosses of extra 

 with extra. 



TABLE XXIV 



Comparing Number of Extras in Low Grade and High Grade Families 



Family Normals Extras Per cent Family 



X 85 3 3.4 A, 



Y 106 1 0.94 Xg 



A 98 3 2.9 



Extras appear with varying frequency both in the first cross of 

 normal with extra and in crosses with later selected generations, as 

 shown by table XXV. 



Normals 



Extras 



Per cent 



93 



1 



1.05 



90 



6 



5.8 







TABLE XXV 









Showing 



Variations in Percentage of 



Extras 









Normals 



Extras 



Per cent 



F,Y 



extra 5 



normal (^ 158 



9 



5.32 



F.Y, 



extra 5 



normal ^ 62 



1 



1.61 



F,A 



extra J' 



normal $ 90 



1 



1.11 



F,A 



extra 5 



normal J' 70 



3 



4.1 



X 



extra (^ 



normal 5 95 



1 



1.03 



F3X, 



extra 5 



normal (^ 106 



6 



5.66 



If selection was a factor in the appearance of extra bristles, Avhen 

 two extras were mated and the extracted normals crossed, one might 

 expect the greater number of extra-bristled flies to appear in the ex- 

 tracted culture, rather than in the normal culture. Such is not the 

 case, however, as extras appear with equal frequency in normal culture 

 and in extracted normal cultures from mating of two extras. 



Nor. from extracted FgXg 101 Nor. bred in mass = F4X5 = 101 

 Nor. -(- 2 ex. == 1.94 per cent. 



Nor. from normal F^Y 127 Nor. bred in mass = FgY = 82 Nor. -\- 

 3 ex. = 3.32 per cent. 



In high-grade cultures where extras have been bred with extras 

 for successive generations, one might expect to find a higher frequency 

 of extra bristles appearing in subsequent generations than in cultures 

 where two extras descended from normals were bred together. This 



