BRISTLE INHERITANCE IN DROSOPHILA 



63 



with the flies there has been found no reason to suspect acci- 

 dental contamination. Fhes with extra bristles w^re occasionally 

 found in this stock. Their frequency is shown in table 1. Vari- 

 ous other stocks were examined and extra bristles were found in 

 smaller numbers. 



TABLE 1 

 Extra bristles found in various stocks 



TABLE 2 

 Percentages of nor- 

 mals in successive 

 inbred generations, 

 selected for in- 

 crease in bristles. 



From the Woods Hole 1912 stock a male with one extra bristle 

 was mated to a female with two extra bristles. Of their off- 

 spring 55.1 per cent had extra bristles. Thirty-three matings 

 of first generation flies with extra bristles resulted in an Fo with 

 90 per cent extra bristles. The subsequent generations pro- 

 duced by inbreeding brothers and sisters in pairs gave higher 

 proportions of extras (table 2). One might suppose that the 

 occurrence of normals in the later generations indicated impur- 

 ity; but in spite of being normal in regard to the group of bristles 

 selected for observation, these flies frequently show extra bristles 

 on other parts of the thorax, and, further, there will be presented 

 evidence indicating that such normal appearing flies may pro- 

 duce all extra children; in other words, that other than genetic 

 causes may prevent the development of potential extra bristles. 



