BRISTLE INHERITANCE IN DROSOPHILA 



65 



TABLE 3 

 Occurence of normals in three mass cultures 



TABLE 4 



Three generations of 

 selection by pairs of 

 normal New York 

 stock to reduce the 

 numbers of extra 

 bristles and test the 

 influence of mating 

 by pairs on the num- 

 bers of bristles. 



between extra females from the first inbred generation, and 

 normal males from the unselected New York 1912 stock, showed 

 in general a dominance of the normal, although less than .5 per 

 cent extras were found. These extras were always of very low 

 grade, + 1 (one extra bristle), while the corresponding inl^red 

 generation of extras showed a range up to +7 (seven extra 

 bristles) and a mode at + 2. If extra bristles were supposed 

 to be due to environmental conditions it would be difficult to 

 account for their general disappearance in this generation. 

 In the following generation, Fo, the extras appear in proportions 

 approximating the simple Mendelian ratio, although the normals 

 are somewhat more numerous than expected. The extras that 

 appear in Fo include higher grades (table 5A). 



A second set of crosses between extras and normals, after each 

 race had been selected for a number of generations, was made. 

 The extras used were from the 9th and 10th generations of in- 

 bred selection. In every cross the dominance of normal was 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 19, NO. 1 



