260 



The Induction of Gene Mutations 



Other Radiation 



Other types of radiation such as ultraviolet light and neutrons 

 have been used to determine their effect as causative agents of 

 mutation. Whiting used, the same technique in studying the 

 effect of neutrons in the production of dominant lethal muta- 

 tions that he had used in X-ray studies. Males were subjected 

 to various dosages of neutrons and were then mated (Fig. 78). 



Fig. 78. Male (left) and female (right) of Habrobracon jnglandis. 

 (Courtesy of Dr. P. W. Whiting; female from the Journal of Heredity.) 



If a dominant zygote lethal was produced, the number of bi- 

 parented females would be less than in the controls and the 

 number of males approximately the same. The results he ob- 

 tained (Table 8) show definitely that neutrons produce domi- 

 nant lethal mutations; actually, they are more effective than 

 X-rays. 



Ultraviolet light is far less satisfactory for studying induced 

 mutations than X-rays, gamma rays, or neutrons because most 

 of the radiation is absorbed by the tissues of the organism and 

 consequently thq penetration of the rays to the germ cells is 

 low. Altenburg and Demerec, Hollaender, Houlahan, and Bishop 

 have devised means of reducing the absorption and have shown 

 that ultraviolet light will increase the frequency of mutations. 

 Altenburg treated cells of the germ tract at the time they form 

 a polar cap in the developing Drosophila egg. As they are 



