Chromosomes and Genes 99 



chromosome (crossover). The definition must contain the character- 

 ization of the gene itself, and that is its ability to mutate into one 

 or more alleles. 



We must ask which facts can be said to prove the existence of 

 the corpuscular, individual gene within the chromosome, the existence 

 of which was extrapolated from the mutant locus. If we carefully 

 survey the facts of genetics, we notice with surprise how few facts 

 demand the existence of the gene. Let me make the meaning of this 

 clear. The corpuscular gene as used in standard genetics must be one 

 or more molecules of a definite substance, different from that of the 

 next gene and the others which are held together in a definite order 

 by some structure or Hnks comparable to the string in a string of beads, 

 or by chemical links, or by electric ones. But it is conceivable that the 

 chromosome is a genetic whole with a complicated structure which 

 changes from point to point as the prosthetic groups do in a protein 

 molecule. In such a structure, that is, a chain molecule, as well as 

 a supermolecule built of individual linked molecules, there are no 

 independent or separate bodies but innumerable points, loci, in which 

 something can change in a chemical or physical sense (i.e., structure 

 or pattern) though leaving the changed group or radical or side 

 chain or part molecule still a part of the whole. The model of this 

 on the unimolecular level would be the stereoisomere. It would 

 certainly be farfetched to call such a sterically displaced group of 

 atoms an independent body, a kind of gene. 



Mazia's (1954) experiments (mentioned in I 2 B a) resulted in 

 breaking up the naked chromosomes of the sperm head into particles 

 of macromolecular size, which are supposed to be held together by 

 metal ions. There is no reason to assume that the particles represent 

 genes. The facts as far as they go may be considered to be a demon- 

 stration of the supermolecular nature of the chromosome. If the inter- 

 pretation is correct, it would mean that supermolecules are built from 

 macromolecules not by utilizing the same bonds which keep the macro- 

 molecule together but by different links. This may result in larger 

 functional units, just as well as if other chemical bonds or links were 

 used. Thus Mazia's results do not affect the theory of the genie 

 material one way or the other. We still have to decide whether 

 genetic facts are available which exclude our view of the loci and 

 mutant loci in the chromosome as patterns in a whole and demand 

 the corpuscular, separate, imbedded gene. 



I can find only a single group of facts which might supply 

 decisive information. The effect of a deficiency for a definite locus 



