SFA'SITINITV OF DROSOPHILA GERM C:i:i.I, STAGES TO X IRRADIATIOX 



Table 5. IVr cent traiislocalioiis followiiiu; irradiation (with IGOO r) of sjx-riri (y sc**' In49 sc*; 

 liw.st p'') in inseminated feinaies ol'diilerent i:;enoiypes and nnder diflerent ronditions 



Females Per cent traiislocalioiis 



Canton-S ?>/ 54/1275=^4-2 



Samarkand 2 1/ 49/ 1 025 = 4 ■ 8 



Oregon-R ?;/ 14/399 =3-5 



Lozenge ?/ 50/944 =5-3 



f 

 Oregon-R $ (starved and desiccated) j/ 50/1027 = 4-9 



f 

 Oregon-R $ (starved and desiccated) ^/+ O., 33/710 = 4-6 



Returning for a moment to the effects of more drastic changes and their 

 effects on mutagenesis, I would like to discuss the extensive work of 

 Sobels'*^' *''^' '*^- **• ^^ and Clark^-. Sobels found, by careful breeding to ensure 

 the sampling of germ cells to be homogeneous at the time of treatment, that 

 exposure of Drusophila to such catalase- and cytochrome-inhibiting sub- 

 stances as sodium azide and potassium cyanide prior to or following X 

 irradiation potentiates X-ray mutagenesis^^'*-' *^'^*' ^^. Clark also obtained 

 an enhancement after injecting flies with sodium azide prior to treatment with 

 an intense dose of X-rays {i.e. 2000 r/minute). Sobels reported that post- 

 treatment of Drosophila males with cyanide significantly enhances the rate 

 of sex-linked lethals induced by X-rays delivered at a high intensity [i.e. 

 2200 r/minute), but not at a low intensity {i.e. 590 r/minute). His work 

 seemed to indicate that the enhancement of X-ray induced damage was 

 greater in spermatids which had been either pre-treated or post-treated than 

 in spermatozoa which had been treated similarly and ^\'as interpreted as 

 showing that substances favouring the accumulation of peroxides enhance 

 X-ray mutagenesis. 



However, since cyanide and azide are non-specific enzyme poisons the 

 results do not indicate whether this potentiation of X-ray mutagenesis is 

 mediated by an inhibition of the catalase or cytochrome systems or both. 

 While Sobels had reasoned that it is probably catalase which is inhibited 

 it had not been ruled out that the cytochrome system was not involved, 

 since Wolsky*^, using carbon monoxide which is a fairly specific inhibitor of 

 cytochrome oxidase in the dark, had shown that cytochromes function 

 in the pupae of Drosophila. To decide this question, inseminated females 

 were pre- and post-treated and pupae containing spermatids \vere pre-treated 

 with carbon monoxide in the dark and irradiated. The different groups of 

 inseminated females were exposed for 5 minutes with carbon monoxide and 

 the pupae were exposed for one hour. During these treatments it was noted 

 that Drosophila is relatively insensitive to the poisonous effects of carbon 

 monoxide. Genetic analyses of their offspring yielded the results shown in 

 Table 6. 



Therefore Sobel's assumption that part of the mutagenic effect of X-rays 

 is mediated by the formation of peroxide radicals, most of which are ordin- 

 arily decomposed by catalase, is borne out by our results showing that 



264 



