112 Nature of the Genetic Material 



a gene consists of subgenes ( genomeres ) which might be separated in 

 mitosis, thus leading to different genomere arrangements, which look 

 like somatic mutation visible as variegation. Clearly this is the same 

 conception as my old one, but applied to the specific case of "unstable 

 genes." The reason for mentioning this is that the authors realized the 

 existence of a group of facts which raise difficulties for the classic 

 concept of the gene, the same group that has recently induced 

 McClintock (1951) to come to conclusions very much akin to my own 

 regarding the non-e.xistence of the corpuscular gene. 



The most elaborate of such theories involving subgenes in a 

 specific case was the theory of step-allelomorphism by Serebrovsky, 

 Dubinin, et al. (1929ff.; see Serebrovsky, 1930), again based upon a 

 group of. facts which seemed to defy the classic concept of the gene. 

 The main point is that different alleles of scute (1st chromosome of 

 Drosaphila) could be arranged in a definite series according to the 

 pattern of bristles which were removed by each allele, that is, the 

 scute effect. In any compound of two alleles only those bristles were 

 removed which were affected in common by each allele. Let ABCD 

 be four different bristles and abed their suppression. The allele sc° 

 may produce the pattern AbcD and the allele sc" the pattern abCD. 

 The compound scVsc^ is AbcD/abCD and, therefore, only the bristle 

 b is missing. If we write only the changed bristles in the compound 



we have — 

 a 



b 



Q 



— The affected areas are steplike, and only the 



b 



common part (b) is affected. Therefore, it is assumed that such a 

 steplike pattern is present in the gene itseff, and a consistent pattern 

 for many alleles was elaborated. The gene, then, would be a body of 

 definite length, made up of a series of smaller elements arranged like 

 a bundle of sticks the ends of which do not coincide stepladder 

 fashion. It is obvious that the authors had vaguely in mind a condition 

 which we shall later discuss as pseudoallelism, though with the ad- 

 dition of the stepladder system. The general point was that behind 

 special genetic phenomena a pattern problem of the genie material is 

 hidden, which clearly goes in the direction of present-day ideas. 



This theory lost its usefulness when it turned out that many of 

 these scute alleles are chromosome rearrangements, and also that the 

 phenotypic facts are not exactly as described (see Raffel and Muller, 

 1940). Nevertheless, the fact remains that the authors of the brilliant 

 idea realized that they were dealing with a body of facts which did 

 not fit into the classic theory of the gene. Actually, the data on scute 

 alleles will be used below to support the newer theories. 



