Questions and Problems 



261 



near the surface of the egg, there was not much intervening 

 tissue to absorb the rays. He pointed out that if ten pole cells 

 were present at the time of treatment and that if a mutation 

 occurred in one, about one-tenth of the sperm cells of the adult 

 should have the mutation. Studying the frequency of lethals 

 in the X chromosome by the CIB method, he found eight cases 



TABLE 8 



Dominant Lethals Caused by Neutrons in Habrobracon 



(From P. W. Whiting, in Science.) 



Fluctuations in number of male offspring are probably due to small numbers 

 involved. 



of these ''reduplicated" lethals from 108 treated males. Demerec 

 and his co-workers reduced the amount of absorption by com- 

 pressing the abdomens of fruit flies between quartz plates dur- 

 ing irradiation. Sex-linked lethals were determined by the CIB 

 method. Although the results were complicated by a high degree 

 of induced sterility due, apparently, to injury through radiation 

 which penetrates the wall of the abdomen, the production of 

 lethal mutations by ultraviolet light of different wave lengths 

 was definitely demonstrated. 



QUESTIONS AND PROBLEMS 



1. Why is it easier to detect recessive visible mutations in the X 

 chromosome by using the attached-X strain than by using a normal 

 strain of Drosophila melanogasterf 



