Chromosomes and Genes 1 1 1 



o. Precursor ideas 



Perhaps the first step in this direction away from the classic gene 

 was made by the author ( Goldschmidt, 1920a, 1927), still within the 

 theory of the corpuscular gene, when he tried to make this theory 

 more flexible and amenable to physiological interpretation by the as- 

 sumption that the gene consists of a definite number of molecules and 

 that mutation changes this number. Thus a series of multiple alleles 

 became a quantitative series of gene molecules. The idea was derived 

 from facts which showed a relation between mutants and multiple 

 alleles, on the one hand, and rates of developmental processes, on the 

 other hand, which could be reduced to simple terms of chemical 

 kinetics by the assumption of a simple relation between genie mass 

 and genie action. The hypothesis allowed the elaboration of a detailed 

 physiological theory of heredity which accounted for many facts of 

 genetics and physiological genetics. If it could be proved that the 

 classic corpuscular gene exists, this theory still accounts for more 

 genetic facts than any other theory of mutation. In addition, it gives a 

 chance of interpreting many genie actions for which other theories of 

 the gene have no explanation. (We shall return to the subject when 

 we study genie action, dosage efiFects, exaggeration phenomenon.) 



Within the Treffer theory it might also be assumed that the gene 

 is a group of molecules and that one hit knocks out one of them (say 

 by denaturalization). Adherents of the target theory have discussed 

 this possibility and have come to the conclusion that this interpretation 

 is impossible because of the alleged facts of return mutation. Actually, 

 I had anticipated this argument when I still believed in the theory of 

 the gene quantity, and had concluded that return mutation must be 

 non-existent or extremely rare. It seems that later developments 

 (reported above) agree with this conclusion. 



I consider these deliberations to be of only historical interest; 

 they are relevant only when the classic theory of the autonomous gene 

 is valid, which I now deny. But the part of the theory which has to do 

 with genie actions of a dosage type will have to be discussed later in 

 its meaning for newer ideas on the nature of the genie material. 



Some other theories that attempted to go beyond the simple gene 

 molecule deserve to be mentioned as precursors of present-day 

 ideas. The first of these, proposed by Eyster and Anderson ( 1924 S.; 

 see Goldschmidt, 1938), tried to account for variegation produced by 

 what formerly were called unstable genes. The general idea was that 



