NATURE OF THE GENETIC EFFECTS 393 



pointlike disturbances, of such a nature as to be capable of changing 

 practically any gene. Now this is just the mode of operation of radiation 

 when it is applied to a complex mixture of organic substances in aqueous 

 solution. 



It was not so surprising, then, that radiation should prove to be efTective 

 in the causation of gene mutations. This being the case, it was also 

 quite in line with expectation that the radiation mutations of genes, like 

 the spontaneous ones, should be found to occur according to a sporadic, 

 pointwise, essentially fortuitous pattern of incidence. This resemblance 

 extended even to the finding that the gene mutations produced by radia- 

 tion in diploid cells involved only one of any two identical genes present 

 (Muller, 1928d). 



A further parallelism lay in the fact that, as had already been shown for 

 the spontaneous gene mutations (Bridges, 1919; Muller, 1920, 1928c; 

 Muller and Altenburg, 1921), the occurrence of radiation mutations was 

 found not to be confined to any given type of cell or period of develop- 

 ment, since analysis of experiments designed to test these questions 

 showed the mutations to be produced in either mature or immature 

 stages of the individual, in females or males, and in germinal or, as first 

 shown by Patterson (1929), somatic cells. It is true, however, that their 

 frequencies of production in some of these different situations did appear 

 somewhat different — a matter to be taken up in more detail in Chap. 8. 

 Now the mutations that were produced in early (primordial or gonial) 

 germ cells necessarily resulted in a whole group of offspring carrying the 

 same mutant gene (Harris, 1929). Similarly, those produced in somatic 

 cells which later proliferated resulted in a whole patch of tissue or part of 

 the body having the mutant gene. 



It should be observed that these cases of the derivation of a visibly 

 abnormal portion of the body from a single mutant cell illustrate by 

 analogy the gene-mutation interpretation of the causation of some 

 malignant growths. If any of these somatic mutations should chance to 

 be of such a nature as, singly or (more likely) in combination, to result in 

 continued unregulated prohferation, a neoplasm or other malignancy 

 would thereby have been induced. In view of the great number of 

 different genes in every cell, the exceedingly diversified character of 

 different gene mutations, and the vast number of cells in the adult body 

 which are still capable of undergoing some proliferation, it would be 

 strange indeed if a gene mutation, or, eventually, a combination of 

 mutations, did not sometimes arise, which conferred on the cell containing 

 it the property of proliferating to an unlimited extent, even in the face 

 of the checks to growth which are continually provided by the regulative 

 morphogenetic influences of the surrounding normal tissues. 



It is not to be expected that additions or subtractions of whole chromo- 

 somes or even of gross parts of chromosomes would, as postulated in the 



