Chapter 16 

 THE INDUCTION OF GENE MUTATIONS 



In the last chapter it was pointed out that gene mutation may 

 be greatly influenced by the environment in which an organism 

 lives. It is natural, then, that geneticists should look for en- 

 vironmental conditions by means of which they can artificially 

 induce the mutation of genes. 



Attempts to induce mutations were begun rather early in the 

 history of genetics. Frequently the results were negative, and 

 the few times there was an indication of positive results, the 

 results were not clear. When there was an indication of posi- 

 tive results mutations sometimes appeared in the controls as 

 well as in the treated material, and sometimes repetitions of the 

 experiment did not substantiate earlier claims. Environmental 

 conditions which were tried included variations in the amount 

 of food, unusual conditions of temperature, moisture, and light, 

 and the subjection of organisms to radium rays and X-rays. In 

 this early period, although most of the work was unsuccessful, 

 Morgan succeeded in obtaining some wing mutations in Dro- 

 sophila by treatment with radium. 



The years 1927 and 1928 mark the beginning of the extensive 

 work on the induction of gene mutations by radiation. During 

 those years, Muller published the results of some X-ray studies 

 in Drosophila for which he was awarded the Nobel prize in 

 1946. Stadler demonstrated the effect of X-rays in producing 

 mutations in plants, and Gager and Blakeslee recorded two mu- 

 tations induced in the plant. Datura Stramonium, by gamma 

 rays from "radium emanation," in addition to a number of chro- 

 mosomal aberrations. Since that time, extensive work on the 

 induc-tion of mutations by radiation has been carried on in a 

 great many organisms. Muller's publication in 1927 can be re- 

 garded as ushering in the radiation program, for it preceded 

 Stadler's by almost a year, and Gager and Blakeslee's studies 

 were concerned more with chromosomal aberrations than with 



243 



