62 



THE CELL AND PROTOPLASM 



feeff). Further the reciprocal experiments 

 of Sitko might be quoted, showing that the 

 frequency of induced point mutations is 

 higher near preexisting breaks. In passing 

 I might point out that one of the methods of 

 increasing the rate of mutation, namely 

 aging of seed (Nawashin) fits much better 

 into such a viewpoint than into any other. 

 Finishing this chapter we might say that, 

 although this line of work is still in its in- 

 fancy, it points in the same direction as the 

 results of the foregoing chapter did : namely, 

 that a mutated locus (acting in the over- 

 whelming majority of cases as a disturber of 

 normal development with the resulting 

 monstrosity called a mutant) is in fact a 

 change in the minute patterns of the parts 

 of a chromosome, a rearrangement or pat- 

 tern-change, and not a change within a 

 discrete particle of molecular order. The 

 same applies, of course, to submolecular 

 units such as sidechains. 



We come now to another group of facts, 

 almost exclusively analyzed in Drosophila, 

 which strongly point in the same direction, 

 facts usually described under the term posi- 

 tion effect. One of the standard dominant 

 loci, in Drosophila, used in all elementary 

 class work is Bar-eye, the prototype of a 

 dominant "gene." A considerable time 

 ago Sturtevant found by an admirable 

 genetic analysis that one of the alleles of 

 Bar, ultrabar, is in fact a so-called Bar- 

 gene, represented twice in the same chromo- 

 some, and so a double-Bar. This made it 

 possible to compare two so-called Bar-genes 

 located in the same chromosome side by side 

 with the same two opposite each other in 

 different chromosomes. The effect of the 

 two constellations was a different one, and 

 this was called a position effect. The term 

 has since been used for all cases in which a 

 change in the chromosomal pattern without 

 a change within an individual gene pro- 

 duces some visible effect. In order to make 

 these cases conform to the conception of 

 position effect and to explain them in terms 

 of genes, it was assumed that the gene inter- 

 acts with its direct neighborhood in func- 

 tioning and therefore functions differently 

 in a new neighborhood (Muller, Offerman). 



Aside from the difficulties which this idea 

 would encounter if worked out in concrete 

 chemical terms, it actually does not work 

 in the majority of cases which were found 

 since, including the Bar-case itself. I must 

 confess that I was very skeptical towards 

 the actual existence of the position-effect, 

 when it first became known. The reason 

 was that, being a convinced supporter of the 

 classic theory of the particulate gene, I could 

 not believe in a phenomenon which would 

 force us to change or even abandon this 

 theory, a necessary consequence which I 

 realized from the beginning. But since 

 that time numerous such pattern-effects, in- 

 explicable in terms of genes have been 

 found. Let us select a few cases of different 

 types from the almost weekly increasing list 

 of pertinent facts, and state in advance that 

 no type of so-called genie action is known 

 which does not also occur in the form of 

 position effect. 



There is first the Bar-case, representing 

 the type of action which is usually ascribed 

 to dominant genes. It is known to-day 

 (Bridges, Muller) that Bar is actually a 

 duplication of a small section of the chromo- 

 some and its multiple allele ultrabar a trip- 

 lication of that section. Then it was found 

 (Dobzhansky) that a translocation of a 

 piece of another chromosome into the Bar 

 region also produces the effect Bar-eye. 

 Finally, the school of Dubinin found a large 

 series of very different translocations with 

 one break at the Bar-locus, or nearby, or 

 even at a considerable distance from it, 

 which always produced the Bar effect. 

 These facts exclude, of course, an interpre- 

 tation in terms of gene-neighborhoods, for 

 these are different in any individual in- 

 stance; and, as a matter of fact, it would 

 require quite a bit of contortionism to find 

 in these facts room for an actually existing 

 Bar-gene. 



A very important point ought to be added 

 to this discussion. Sturtevant, who is cer- 

 tainly not suspected of heterodox views re- 

 garding the gene, was forced to conclude 

 from his old genetic analysis of the Bar 

 case that the "Bar-gene" has no wild-type 

 allele. This rather prophetic conclusion is 



