IRWIN I. OSTER 



to break and form bridges about as often as an X chromosome in either male 

 or female, while females heterozygous for a more breakable ring-X chromo- 

 some would have been found to be more radio-sensitive than females with 

 two rod-X chromosomes. 



It is planned that this type of analysis will be extended to include the 

 effects of other mutagenic agents on individuals of diverse chromosomal 

 make-up and the effects of radiation on specially-constructed stocks of females 

 whose X chromosomes are permanently attached to each other. If our inter- 

 pretation is correct, these should behave more like males than normal females 

 having two detached X chromosomes following an exposure to X-rays. 



/ wish to thank Professor H. J. Midler for the many stimulating discussions which 

 we had during the course of this work. I should also like to express my appreciation to 

 Mrs. Astrid Cicak who helped with many of the technical aspects of the experiments. 



REFERENCES 



^United Nations Scientific Committee on the Effects of Atomic Radiation Report 

 to the General Assembly, Official Records : Thirteenth Session Supplement No. 1 7 (A/3838), 

 New York, 1958, p. 22 



2 0sTER, I. I. and Cicak, A. Drosophila Inforin. Serv. 32 (1958) 143 

 ^PoNTECORVo, G. and Muller, H.J. Rec. Genet. Sac. Amer. 9 (1940) 165; Genetics 



26 (1941) 165 



^Muller, H.J. and Pontecorvo, G. Rec. Genet. Sac. Arner. 10 (1941) 157; Genetics 



27 (1942) 157 





271 



