284 



GENETICS 



wise known to exist and, in fact, were first discovered 

 in moths by Doncaster. In these cases it is the fe- 

 male instead of the male that possesses the mechanism 

 whereby the character in question can be present only 

 once. 



Black Male Barred Female 



Gametes 



Z Z 



z 



zo 



Gametes 



Z O 



z z 



z o 



FIG. 89. Sex-linked inheritance, with the female heterozygous. 

 Reciprocal cross to that shown in Fig. 88. The "barred" char- 

 acter is indicated by the underscored gametes. 



For example, "barring" is a dominant sex-linked 

 trait in poultry, as shown in Figures 88 and 89. 



In the cross shown in Figure 88 all the males and half 

 the females in the F 2 generation are barred while in 

 the reciprocal cross shown in Figure 89 the Fj males are 

 barred because they have a ^-chromosome from their 



