244 The Induction of Gene Mutations 



gene mutations. Muller's studies surpassed the previous work 

 by developing special techniques that eliminated the question- 

 able elements of the earlier investigations. 



X-rays and Radium 



X-rays and radium are the most effective means of inducing 

 gene mutations in animals and plants. Figure 74 illustrates a 



Fig. 74. A gene mutation in Oenothera induced by radon. A rosette 

 (right) of mutant pannosa of Dr. W. H. Brittingham and one of Oenothera 

 Lamarckiana (left) not exposed to radium emanation. (Courtesj^ of Dr. 

 G. H. Shull.) 



leaf mutation in Oenothera induced in Brittingham's cultures by 

 radon. The organism is- placed near the window of an X-ray 

 tube, or small tubes containing "radium emanation" are placed 

 alongside the tissue to be treated. The time of exposure has 

 varied in the different experiments and, to be effective, differs 

 with the organism to be studied. 



The relation between X-ray dosage and the production of 

 mutations is considered by many geneticists to be very simple. 

 Studies of this nature have largely been carried out by noting 

 the number of lethal mutations produced in Drosophila melano- 

 gaster after subjecting the flies to different amounts of X-rays 

 or to the same amount over different periods of time. Other 



