148 RADIATION GENETICS 



mutants and thus show up in only a few animals per generation, the detection of which 

 would be statistically difficult. 



Reproductive performance. — Here, too, there appears to be a shortage of data, with 

 the exception, of course, of the studies on dominant partial sterility discussed earlier. 

 As noted by Russell and Russell, 1138 there will be a small percentage of the progeny 

 of irradiated parents that will be completely sterile. Minor reductions in reproductive 

 performance most certainly will be difficult to detect and will require good sampling 

 statistics. The author has a small quantity of data for lifetime performance. The 

 experimental group, the progeny of C57BL/6 males subject to 5 r/day of Co 60 gamma 

 radiation for 120 days, shows a 7.5 per cent drop in average size of litter and a slightly 

 more rapid senile decline in productivity. Since only ten breeding females were 

 sampled in each of the two groups, no real significance of the data can be claimed. 

 The study was done on a pilot basis in the period 1956-1958 to test the effects of 

 protracted irradiation on the induction of mutations affecting viability and reproduc- 

 tion and to explore the attendant statistical problems (which are many). It can be 

 noted that the careful initial pairing of the breeding stock by age, for experimentals and 

 controls, will automatically lead to a high degree of comparability of the data, litter 

 by litter, throughout the reproductive lifetime. At the same time, changes in the 

 interval between litters will become apparent, if this is to be one of the manifestations 

 of genetic damage. 



Behavioral traits. — There are no data on radiation-induced mutations that affect 

 behavioral characteristics, although attempts to detect genetic damage of this type are 

 being made by Green. 481 



PROTECTION AGAINST INDUCED GENETIC DAMAGE 



Basically, there are two principal methods of approaching radiation protection : 

 preventive therapy and supportive therapy. The latter is typified by the successful 

 use of postirradiation injections of bone marrow to improve survival. Bone-marrow 

 therapy replenishes the animal's hematopoietic tissues during a critical period in the 

 acute syndrome. Postirradiation supportive therapy appears to offer nothing to 

 the geneticist interested in reducing the genetic hazards of radiation. 



Preventive therapy does hold promise. In this case, treatment is required in the 

 immediate preirradiation period or even during exposure. Various chemicals have 

 been tested along with modifications of oxygen tension. The theory behind the use of 

 chemotherapeutics is that they act to reduce oxygen availability, quench active radical 

 transport, or generally act as a competing target system for the initial events of energy 

 absorption. 



While much effort has been spent on radiation-genetic protection studies with 

 microorganisms, 591 very little has been done with mammals. Hypoxia was tried by 

 Russell et al. 1136 as a means of reducing the induction of dominant lethals in X-rayed 

 male mice. The animals were exposed to 800 r while in a chamber flushed with 



