THE FUNCTIONAL ORDER 



The gene as a unit; sexual digression. Our bacterium exhibits 

 sexual processes. When males are mixed with females, they con- 

 jugate. The chromosome of the male is injected slowly into the 

 female, the process lasting around one hour. If the couples are put 

 in a Waring Blendor, the friction forces separate the partners, and 

 conjugation is interrupted. If this is done at intervals, one finds 

 that each gene of the male enters the female at a given fixed time, 

 and that the various genes always enter in the same order. This 

 allows us to locate the place of each gene on the chromosome. This 

 order can be verified by the classical tests of genetics, namely, the 

 determination of the frequency of exchange of one piece of a 

 chromosome for another. This gives a measure of the relative dis- 

 tance of the genes. 



When these types of experiments are performed, one finds: 



1. that the characters of the male can be transferred to the female. 



2. that the three "genes," z, y, and i, controlling the utilization 

 of lactose, are closely associated or linked. 



As already seen, the different genes, i+, z + , y + , can mutate 

 independently, and all possible types of combination are found. 

 Are these genes parts of the same functional unit, or do thev repre- 

 sent different functional units? How can we know that the units 

 are different? What justifies the use of the term "unit"? 



Altered enzymes. It is supposed that a gene, or its corresponding 

 template, produces a protein, as a whole, by a sort of zipper-like 

 mechanism. Let us now consider the gene z (Figure 16). The 



a+ b + 

 1 normal gene 



a- b+ . , 



— 1 1 mutation A 



b- , „ 



' I mutation 8 



Figure 16. Gene Mutation. 



The normal gene possesses the structure a+ b+. A point mutation, a replace- 

 ment of one base pair by another, can take place on various sectors of the 

 gene, for example in a (a+ >■ a~) or in b (b+ >■ b~). 



[43] 



