THE FUNCTIONAL ORDER 



Variations. This original model can give rise to hereditary vari- 

 ants, to mutants belonging to various categories: 



(a) The bacteria able to synthesize /5-galactosidase may give rise 

 to variants unable to perform the synthesis; z+ being the symbol for 

 the character carrying the information for the galactosidase, the 

 mutation is z+ ±^ z~. 



(f 



• /3-galactosidase 



9 



4 zygote 



O /3— galactoside permease 



Figure 14. Genes z and y as Independent Units. 



The z and y genes control the synthesis of /3-galactosidase and /3-galactoside 

 permease, respectively. 



1. The bacterium is z+ and y+: both enzymes are manufactured. 



2. The bacterium is z+ and y~: only /3-galactosidase is produced. 



3. The bacterium is z~ and y+: only permease is formed. 



4. The zygote resulting from the injection of the male chromosome z+ y~ 

 in the z~ y+ female manufactures both enzymes, despite the fact that the genes 

 z+ and y+ are located on different chromosomes (position trans). 



(b) The bacteria able to perform the synthesis of permease may 

 give rise to mutants unable to perform the synthesis of permease; 

 y+ being the symbol for the character carrying the information for 

 the synthesis of permease, the mutation is y+ ^y~ (Figure 14). 



[41] 



