THE FUNCTIONAL ORDER 



X X X X X ^ 



v- X X X 



2+ X X 



I I 5^ 



X X X 



X ^X X "" X 



^ X X X > 



cr 



zygote I 



Figure 18. The Repressor. 



I. The constitutive male i~ does not manufacture enzyme in the absence of 

 an inducer because it is z~. The inductive female i+ does not manufacture 

 enzyme in the absence of inducer, despite the presence of z+, because a re- 

 pressor is present (repressor is represented by crosses). The corresponding 

 zygote (zygote I) does not produce enzyme in the absence of an inducer, 

 despite the presence of the constitutive gene i~, because the cytoplasm of the 

 inductive female contains a repressor. The gene i+ is dominant. 



II. The inductive male does not manufacture enzyme in the absence of an 

 inducer because a repressor is present. The constitutive female does not manu- 

 facture the enzyme because it is z~. The corresponding zygote (zygote II) 

 will produce enzyme for a limited time (see next part of figure), because the 

 z+ gene coming from the male has entered into a constitutive cytoplasm (devoid 

 of repressor). 



The two zygotes (I and II) have the same genetic constitution, but zygote I 

 has an inductive cytoplasm (the female is i+), whereas zygote II has a consti- 

 tutive one (the female is i~). 



[47] 



