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 F2 indi\dduals was apterous. In fact, the F2 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 cT; 



Fi wild-type 9 + Fi star dichoete cf . 



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.— F2, F3 and F^ star 9 (jr~-) + ^2, Fs, and F4 wild-type cf (- ) 



S'4- 



Table SS.—FiStar 9 r-T-^^+ Fi star & (^r-^^ 



V+ aJ \-\- aJ 



LOCUS OF APTEROUS. 

 An opportuinty for determining the locus of apterous was provided 

 by the above material. All attempts to back-cross the F2 star females, 

 a majority of which were heterozygous for apterous, 



(^:-±\ 



\+ Op/ 



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

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



