98 



HEREDITY AND SEX 



THREE SEX-LINKED FACTORS 



When three sex-linked factors exist in the same 

 chromosomes, we have a method by means of which 

 the " crossing-over " hypothesis may be put to a further 

 test. Sturtevant has recently worked over the evidence 



I 7 



G.' 



H.' 



FIG. 51. A-D, YW and GR that enter (A), crossing over to give YR 

 and GW as seen in D. E-Ei, no crossing over. F-Fi, crossing between WM 

 and RL. G-Gi, crossing between YW and GR. H-Hi, double crossing over 

 of YWM and GRL, to give YRM and GWL. 



for a case of this kind. He analyzed the data of the 

 cross between a fly having gray color, red eyes, long 

 wings, mated to a fly with yellow color, white eyes, 

 and miniature wings. The relative location of these 

 three factors is shown in the above diagram (Fig. 51, 



