238 



THE SECOND-CHROMOSOME GROUP 



CHROMOSOME CARRYING APTEROUS. 



The apterous character was distributed at random with respect to 

 both eosin (first chromosome) and dichsete (third chromosome). Not 

 one of the star F 2 individuals was apterous. In fact, the F 2 ratio of 

 258 star : 128 wild-type : 63 apterous : star apterous approached 

 the 2:1 : 1 : ratio expected if apterous is in the second chromosome 

 (table 86). There was observed a very free crossing-over between 



TABLE 86. PI, cream c 9 (heterozygous for apterous) X star dichcete cf; 

 F\ mid-type 9 + F\ star dichcete tf . 



cream c and apterous, and this fact, in connection with the star apter- 

 ous result, proved that the apterous mutation had been present in the 

 cream c female, which was presumably heterozygous for it. That this 

 appearance of apterous is due to a second and independent occurrence 

 of the act of mutation in the apterous locus can not be doubted. 



TABLE 87. F 2 , F z and F 4 star 9 (x^O + ^2, F s , and F 4 wild-type cf 1 (- ). 



\-j a n / ^ {* 



TABLE 88. F 4 star 9 



+ & 



F * star cf 



LOCUS OF APTEROUS. 



An opportunity for determining the locus of apterous was provided 

 by the above material. All attempts to back-cross the F 2 star females, 

 a majority of which were heterozygous for apterous, 



+ 



by apterous males failed as expected, because of the sterility of the 

 apterous males. However, a few matings between such females and 



