256 



RADIATION HIOLOGY 



Each of the 79 lothals rccordctl in 'I'ahle 7-1 was t(^stod for position on 

 the X chromosome and found to he unaccompanied by disturbances of 

 crossover frequency with neifj;hboring loci. The following conclusion 

 was drawn: "Ultraviolet light therefore produces no inversions or other 

 chromosomal changes that are detectable from changed crossover values. 

 In this respect, the effect of ultraviolet light differs markedly from that of 

 X rays" (Altenburg, 1934). 



Table 7-1. Summary of Ai.tenburg'.s (1934) Drosophila Data in Which 

 Ultravioi.kt Radiation Was Shown' to Be Mutagenic in Nature 



" From th(> 222 control eggs, 13,063 Fi females were tested; from the 239 treated 

 eggs, 14,059 Fi females were tested. 



The development of the abdominal exposure techiii(iue by Reu.ss (1935) 

 demonstrated the feasibility of inducing mutations in the matiu-e sperma- 

 tozoa of Drosophila. Mackenzie and :\Iuller, using this method, have 

 confirmed and extended the earlier findings of Altenburg, particularly as 

 concerns the comparison of the effects of ultraviolet and X rays (MuUer 

 and Mackenzie, 1939; Mackenzie and Muller, 1940; Mackenzie, 1941). 

 The filtered radiation employed consisted of wave lengths above 280 m^u, 

 a (luality of radiation less damaging physiologically than the shorter 

 wave lengths. A dose of 2 X 10'^ ergs/mm^ w^as found to be optimum 

 for the study, since an appreciable frequency of sex-linked lethals (about 

 3 per cent) was induced without an accompanying high degree of sterility 

 or mortality. Higher doses raised the frequency of lethals to 9 per cent, 

 but the sterility was disproportionately increased, making extensive 

 observations difficult and (juantitative comparisons unreliable. The 

 principal results of these studies were the following: 



1. No translocations affecting the Y, II, and III chromosomes were 

 found in a population which had a frequency of sex-linked lethals of 4.3 

 per cent. Such a fre(iuency would be induced by an X-ray treatment of 

 about 1300 r. The authors estimate that, in the number of culttn-es 



