THE HEREDITARY ORDER: GENETIC INFORMATION 



pyruvic acid appears in the urine. The I.Q. of these persons is 

 generally lower than 10. They are idiots, unable to think. This is, 

 however, not important in this analysis. What is important is that 

 the enzyme present in normal human beings and responsible for the 

 normal pathway of phenylalanine is missing in the phenylpyruvic 

 idiots. 



Long before the specific alteration responsible for a mutation had 

 been chemically known, and long before the specific responsible 

 enzyme had been identified, the site of the biological alteration, as 

 already stated, had been located on the chromosome. The responsible 

 chromosomal structures were called ge7}es and described as units of 

 variation. 



The problem was of course to identify the substrate of the 

 hereditary variation, that is, to identify the nature of the entity 

 controlling the production of an enzyme. This was accomplished 

 by the study of bacteria. 



The Genetic Material Identified 



Transformation. Alany bacteria possess an outer layer, or 

 capsule, which is a specific polysaccharide. The agent of pneumonia, 

 the Piieimwcoccus, exhibits many varieties or types. The capsule of 

 each of them is built of a specific polysaccharide in which the 

 nature of the glucidic subunits are difl^erent. The polysaccharides 

 are easy to identify, for a polysaccharide injected into an animal 

 elicits the formation of a specific protein called an antibody (Figure 

 3). An anti-III-antibody combines specifically with the poly- 

 saccharide III and not with polysaccharide II. It agglutinates bac- 

 teria of type III and not of type II. 



Sometimes, as a result of a sudden change, a mutation, a Piieim70- 

 cocciis loses the ability to produce its specific polysaccharide. When 

 this capsuleless, polysaccharideless bacterium, originally of type II, 

 for example, is grown in the presence of extracts of type III bacteria, 

 one recovers capsulated bacteria of type III. Something present in 

 the extract of type III bacteria has trmisfoiined a capsuleless, 

 originally type II bacterium into a capsulated type III. The extract 

 of type III contains the "information" for the synthesis of type III 

 polysaccharide, and this information can be transferred to a bac- 



[17] 



