EFFECT OF HETEROZYGOSIS ON DROSOPHILA 



469 



TABLE 3 



TABLE 4 



Standard deviation of stock, 0.81 grades; of outcrossed, 0.84. 



In the totals and averages the number of spongy winged flies 

 were not included, because the position of this grade in the 

 series was uncertain, but the number of these flies was negligible. 



It will be seen that here, too, the rather unexpected result 

 was obtained, that not only was there no evidence of contami- 

 nation but the outcrossed was, if anything, less normal than the 

 stock, and did not show a greater variability. 



It should be mentioned that the same result had previously 

 been obtained in the case of the character dachs legs, when 

 comparisons were made between stock flies and outcrossed flies 



S dj c ba^ 



derived from the race 



In this case, however, only a 



b p V a sp 



few flies were examined, and those of the outcrossed race had 

 not been freed from the other mutant factors, which were pres- 

 ent in heterozygous condition. 



2 Muller, H.J. The mechanism of crossing-over. American Naturalist July, 

 1916. 



