532 RADIATION BIOLOGY 



(unpublished data of 1931) had found a significant although small produc- 

 tion of translocations following spermatozoon treatment: six transloca- 

 tions appeared among 1965 tested gametes in the ultraviolet series (which 

 at the same time gave 41 lethals in 12,236 X chromosomes) and no trans- 

 locations among 1695 tested gametes in the controls (which gave only 

 3 lethals in 12,372 X chromosomes). One translocation was reported by 

 MuUer (1941a) and another by Demerec, Hollaender, et al. (1941) among 

 offspring from treated spermatozoa. Slizynski (1942) reported finding 

 deletions associated with the lethals obtained by MuUer by means of ultra- 

 violet treatment of spermatozoa, in an abundance comparable to that 

 among X-ray-produced lethals. However, nearly all these involved losses 

 of only one or two bands, thus being of so small a size that according to 

 some cytologists the determination would often lose precision. Exami- 

 nations by P. N. Bridges of 13 lethals produced in spermatozoa in work of 

 MuUer (1941a) failed to yield any certain deletions. 



Kaufmann and Hollaender (1946) reported a significant production of 

 dominant lethals (12 per cent) by ultraviolet treatment of Drosophila 

 spermatozoa and, by analogy with the known X-ray studies, interpreted 

 them as probably results of single breaks. Similarly, in poultry a fre- 

 quency of about 50 per cent of dominant lethals which killed the embryo 

 in the blastoderm stage was produced by ultraviolet treatment of the 

 spermatozoa in vitro (Muller and F. A. Hays, 1944, unpublished data). 

 McQuate (1950) found that sex-chromosome losses, giving viable off- 

 spring and presumably caused by single breakage although lagging was 

 not excluded, were produced by ultraviolet treatment of Drosophila 

 spermatozoa with apparently only slightly lower frequency than by a dose 

 of X rays of comparable effect in producing point mutations. (No cases 

 of breakage with healing, giving terminal deletions, were found, however, 

 although they could have been detected.) That the chromosome losses 

 in these experiments were in fact caused by breakage was indicated by 

 Faberge and Mohler's (1952) finding that, when Drosophila spermatozoa 

 containing ring X chromosomes were irradiated, there was an especially 

 high rate of loss of the sex chromosomes, causing inviable offspring (the 

 viable losses not being detectable under the conditions of this experi- 

 ment). These inviable losses were evidenced by the reduction in the 

 relative number of daughters. However, a comparison with X rays 

 could not be made because the dose used was not determined in terms of 

 its production of recessive lethals. 



That ultraviolet applied to Drosophila spermatozoa is distinctly less 

 potent in causing translocations than is a dose of X rays giving the same 

 frequency of lethals was shown in extensive tests by Muller and Mac- 

 kenzie (Muller and Mackenzie, 1939; Mackenzie and Muller, 1940). 

 This conclusion was confirmed and extended by cytogenetic analysis of a 

 group of 70 sex-linked lethals, derived from ultraviolet treatments of 



