236 



GENETICS 



cross together from one parent they will stay together 

 in the offspring, and if they enter from separate parents 

 they remain separate in the offspring. 



t 



ft* 



ft* 



ft* 



GL 



bv 



FIG. 68. Checkerboard to show the result of crossing a gray-long, 

 black-vestigial hybrid fly back to a black-vestigial recessive. 

 G = gray-body ; L = long-wings ; b = black-body ; v = ves- 

 tigial wings. 



3. THE MODUS OPERANDI OF LINKAGE 



The way linkage works out may best be made clear 

 by illustrations from Morgan. When an ordinary 

 wild-type fly with gray body and long wings is crossed 

 with a fly showing the two mutations of black body and 



