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 I 



vfl 



E i 



9/?' 





' H' 



FlG. 51. — A-D, YW and G/2 that enter (.-1), crossing over to give YR 

 and GW as seen in Z). E-E\, no crossing over. F-Fj, crossing between WM 

 and /SL. G-Gi, crossing between YW and G/2. H-H\, double crossing over 

 of YWM and GRL, to give FfiJlf 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, 



