Radiation-Induced Structural Chromosome Changes 



187 



Lewis John Stadler (1896-1954) 

 is noted for his studies on the nature 

 of mutation and of the gene (see p. 

 ix). He and H. J. Muller discov- 

 ered independently the mutagenic 

 effect of X rays. {From Genetics, 

 vol. 41, p. 1, 1956.) 



QUESTIONS FOR DISCUSSION 



13.1. After both are exposed to the same amount of radiation why should tissue, 

 which is only about ten times as dense as air, contain about one thousand times 

 more ions than air? 



13.2. What evidence can you give to support the view that the ions causing breakage 

 need not always attack the chromosome directly? 



13.3. Does the observation that the volume of a chromosome is variable under dif- 

 ferent conditions mean that it has an inconstant gene content? Explain. 



13.4. Do you suppose that chromosomes exposed to X rays are more likely to under- 

 go structural change when they are densely spiralized than when relatively un- 

 coiled? Why? 



13.5. Discuss the role of heterochromatin in changes involving chromosome number 

 and chromosome shape. 



13.6. Do you suppose that the oxygen content of a space capsule can affect the 

 mutability of Drosophila passengers? Explain. 



13.7. Discuss the relative efficiency, per r, of small doses of X rays and of fast neu- 

 trons in producing structural changes in chromosomes. 



13.8. Do you suppose that the mutability of ultraviolet light threatens man's survival? 

 Explain. 



