GENE MUTATIONS AND EVOLUTION 83 



Again, are the mutations resulting from chromosome 

 breakage essentially "position effects," or are they of the same 

 type as deletions and deficiencies, save that they are of less 

 extent or degree; injuries that do not result in complete de- 

 struction of genes, but only in that reduction in their effec- 

 tiveness commonly seen in gene mutations? 



If "gene mutations" should turn out to be simply position 

 effects, this would require a rewriting of extensive chapters 

 of genetics. In particular it would obviously have a devastat- 

 ing effect on the theory that these are the basic factors in 

 evolutionary change. They would not be changes in the 

 constitution of individual genes at all. They would be simply 

 further illustrations of the known fact that the effects of a 

 particular gene depend on the conditions under which it 

 operates. A new class of such conditions is added to those 

 before known; namely interaction with genes that are in 

 close proximity within the chromosome. A gene removed 

 from the normal grouping and brought into close relation 

 with a new set of genes acts in a different manner from 

 before ; as the facts show, it commonly operates less efficiently, 

 yielding reduced effects. The so-called multiple allelomorphs, 

 supposed diverse modifications of the same gene, would be, so 

 far as due to "mutation," simply the same gene in different 

 positions with relation to other genes. 



The general effect of such changes of gene action with 

 change of position would be to increase the transformism and 

 diversification of organisms by giving rise to many weakened 

 and abnormal types, such as are commonly seen in mutated 

 stocks. But their relation to progressiveness in evolution 

 would completely evaporate. They would not supply the new 

 genes with changed constitution that progressive evolution 

 requires. They would have the same kind of relation to 

 progressive evolution as have the other changes in the struc- 



