144 RADIATION GENETICS 



to obtain with a high degree of accuracy among most Western nations. Unfortunately, 

 comparable data for laboratory animal populations are not generally available, even 

 though many of the laboratory animals enjoy a standard of living far superior to that of 

 the civilization that maintains them. 



The importance to be placed upon these data is emphasized by the fact that the 

 most widely accepted and quoted baseline predictions of the radiation hazard to man 

 are those provided by Crow, 231 involving an expansion of the analysis of Morton, 

 Crow, and Muller, referred to above. These calculations, although ingenious, 

 require the mixed application of parameters from Drosophila, mice, and men. As they 

 stand, they are in need of updating and revision, but, basically, the calculations require 

 careful evaluation for populations of laboratory mammals. In addition, the genetic 

 analysis of the progeny of the survivors in Hiroshima and Nagasaki was largely restricted 

 to data on quantitative anthropometry, morbidity, and mortality. 939 



In general, the basic techniques of breeding employed for the detection of qualita- 

 tive changes can be used for the study of the more subtle quantitative expressions of 

 damage. In many instances, the two types of data can be obtained concurrently. 

 The analytic procedures are more complex, however, and thoughtful statistical design 

 and analysis are required. The key to success is no longer a matter of overcoming the 

 issue of events of low probability by sheer weight of numbers, but rather overcoming 

 the problems of ordinary random fluctuations. 



Sex ratio. — Prior to a discussion of the evaluation of mortality statistics, brief 

 mention should be made of studies of sex ratio. This is a semiquantitative trait that 

 does not require any specialized approach. This parameter has become a con- 

 troversial issue since Schull and Neel 1170 reported a significant shift in sex ratio among 

 the progeny of the survivors at Hiroshima and Nagasaki. Shifts in sex ratio have not 

 been uniformly seen among the progeny of irradiated mice. 1128 A very recent report 729 

 also indicates that the sex ratio of mice remains substantially unaltered following single 

 and fractionated exposure of the male parent. An earlier preliminary report by 

 Kalmus et al. 676 did indicate a deficiency of female offspring from irradiated male mice 

 for litters sired within 40 days of the exposure. The shift in sex ratio was in the direc- 

 tion of genetic expectation, but this study has apparently not been confirmed. It can 

 be suggested that man may be more sensitive to the induction of sex-linked lethals by 

 radiation. Since the X chromosome of man carries more recognizable detrimental 

 genes than have been noted in the mouse, man may have a qualitatively different 

 genetic potential for induced genetic damage. 



Viability. — The general term viability is chosen to cover the full range of mortality 

 periods: stillbirths, neonatal deaths, infant or preweaning deaths, and adult mortality. 

 Data on these traits are scattered and incomplete. Russell, 1128 in his review of the 

 early literature, has indicated that an increase in stillbirth rate and mortality to the 

 time of sexual maturity has been observed among the progeny of irradiated male mice 

 for litters sired in both the pre- and poststerile periods. Similar observations have been 

 made with guinea pigs. 1289 



