846 RADIATION BIOLOGY 



The only data that can be analyzed with regard to this factor are those of 

 Hertwig (1938a) and she tabulates only the results for partially sterile 

 male progeny. In these she found 12 partially steriles in 88 offspring 

 from matings made 1-8 days after irradiation and 2 partially steriles in 

 24 offspring from the 8- to 14-day matings. As far as these data go, they 

 are in agreement with the above assumption, but they are obviously not 

 extensive enough to be considered a satisfactory test. 



The information obtained by Snell (1939) on the incidence of partial 

 sterility in the offspring of presterile-period matings of male mice irradi- 

 ated with fast neutrons is also given in Table 12-9. As would be expected 

 from their effect on chromosome breakage in other organisms, neutrons 

 appear to be more effective than X rays in producing partial sterility, but 

 it is clear that data obtained with modern methods of irradiation and 

 dosimetry are needed to establish the ratio of effectiveness. 



The incidence of partial sterility in offspring of X-irradiated female 

 mice was determined by Snell and Ames (1939), as shown in Table 12-9. 

 Comparison of the result with incidence in offspring of irradiated males is 

 difficult because there are no data from males exposed at this dose level, 

 and the data from higher doses are, as has already been pointed out, not 

 adequate for establishing the frequency-dose curve. However, the inci- 

 dence of partial sterility in the offspring of females appears to be lower 

 than what would be expected from males irradiated with the same dose. 

 Since, in Drosophila, the incidence of translocations in irradiated female 

 germ cells is much below that in irradiated sperm (Glass, 1940), some 

 consideration should be given to the possibility that the frequency in 

 progeny of irradiated female mice may be even lower than the results of 

 Snell and Ames indicate. The fact that two of the three partially sterile 

 animals found in the 151 offspring came from the same female suggests 

 the possibility that this female was herself carrying dominant partial 

 sterility. As she had only one other offspring that was tested, no definite 

 conclusion can be reached. This uncertainty, coupled with the limited 

 total of only three partially sterile animals obtained, still leaves some 

 latitude for assuming that in mice, as in Drosophila, translocation induc- 

 tion in females may be much less frequent than in males. 



As Hertwig (1935, 1938a) first clearly showed, Table 12-9, there is no 

 evidence for the occurrence of radiation-induced partial sterility in the 

 offspring of poststerile-period matings of X-irradiated male mice. This 

 indicates either that translocations are not induced in spermatogonia or 

 that they occur and are eliminated by germinal selection. However, 

 elimination seems unlikely in view of the fact that translocations are 

 easily transmitted through descendant generations. The hypothesis of 

 lack of occurrence, therefore, seems to be the more plausible one to 

 adopt. Since there is evidence, from the great reduction in number of 

 spermatogonia following irradiation, that chromosome breakage resulting 



