THE FUNCTIONAL ORDER 



d 



0+ b'*" in position CIS 



zygote 

 0+ b"*" in position trans 



Figure 17. The Gene z as a Unit. 



When the gene is z+ (a+ b+), /3-galactosidase is synthesized (lower-left corner) 

 and a+ b+ are located on the same chromosome (position .cw). 



The mutated gene a+ b~ (male) or a~ b+ (female) is unable to "produce" 

 the enzyme. The heterozygote (lower-right corner) does not manufacture the 

 enzyme: a+ and b+ are located on a different chromosome (position trans), and 

 there is no complementary relation. 



this case, the information carried on two separate genes — that is, in 

 position trajis — is useless. The structure z can function only as 

 a unit. In the modern terminology, z is a cistroii. The locus z thus 

 contains the genetic information for the molecule of /3-galactosidase. 

 A number of experiments have provided good evidence that it con- 

 tains all of this information. The gene z functions as a whole. In 

 order that a protein be synthesized, all of the information has to 

 be present in one and the same structure (position cis). There is 

 no complementary relation between two different mutants of the 

 same gene. The gene, or better the cistron, is therefore a unit of 

 information and of function. 



By the same technique, it is possible to show that the synthesis 

 of the permease is controlled by a unit y, different from the unit z. 

 Finally, inductivity is itself controlled by another unit, i, different 

 from y and z. 



[45] 



