THE NATURE OF THE GENE 295 



a statement in exact physical terms of what was more or less 

 clearly implied in all other theories of the gene. 



3. THE GENE AS AN AGGREGATE OF DIFFERENT PARTS 



In opposition to the idea that the gene is a single chemically 

 active molecule or a group of such, the view has been expressed 

 that certain groups of facts require for their explanation the 

 assumption that the gene consists of different separable parts, or 

 subgenes. 



A. The Genomere Hypothesis of Anderson and Eyster 



This theory was invented by Eyster and Anderson (1924, 

 1925, 1928) to account for the facts of variegation produced by 

 what are now called unstable genes. The facts have already 

 been reported and analyzed in connection with Demerec's and 

 Correns' interpretation. Anderson and Eyster assume that 

 those facts can be explained only if a quantitative segregation of 

 parts of the gene takes place during development. The gene, 

 then, is regarded as composed of a constant number of genomeres, 

 or gene elements, which may or may not be chemically identical. 

 The usual genetic difference between pigmented and pigmentless 

 forms is given in the genomeres, all the genomeres C having 

 mutated into c. If, however, only a certain number of geno- 

 meres mutate from C to c, an unstable gene with two types of 

 genomeres is produced. This gene might be divided into its 

 genomeres in somatic mitoses, producing different combinations 

 of genomeres up to a complete separation of the two types C and c. 



It is obvious that this interpretation is a slightly different way 

 of describing the behavior of the "sick" gene. It agrees with 

 Correns and with Goldschmidt in so far as a quantitative element 

 within the gene is required, which may be conceived as numbers 

 of side chains (Correns), numbers of molecules (Goldschmidt), 

 or numbers of genomeres (Anderson). Any of these or similar 

 conceptions will account for the facts, but also any other explana- 

 tion of genie changes. It can therefore not be considered that the 

 facts lead necessarily to the genomere theory. 



B. The Hypothesis of the Serebrowsky School 



We have reported upon the case of step allelomorphism in the 

 scute series of allelomorphs in Drosophila. The facts are 



