GENETIC EFFECTS 7 



many but not all respects — witness recent studies on human hemoglobin — basic genetics can 

 best be studied in such organisms. It is inevitable that some of the most important conclusions 

 that are applied to man will have to be derived in the first place from our basic knowledge of 

 the effects of radiation on other organisms. 



To determine the amount of exposure of human populations to radiation, further studies 

 are needed of the dosages received by various parts of the body — especially the gonads — 

 from such sources as medical, industrial, research, and military uses of radiation, whether 

 these be external or internal to the body. It is also necessary to know the physical character- 

 istics and the distribution in the body of the various types of radiation. And, although it is 

 not for this Committee to say how we might best attain it, we need further knowledge of the 

 ways in which dosages may be reduced without sacrificing important economic gains and the 

 advantages derived from the proper use of medical radiations in diagnosis and therapy. 



To determine the consequences of radiation exposure for present and future generations, 

 information at many levels is needed. Investigations designed to obtain such information may 

 be classified under two general headings, though many individual projects may come under 

 both, or fall between. 



1 . Investigations needed for early improvement in estimates of radiation exposures from 

 given practices and their consequences. These are obviously necessary as a basis for wise 

 policy decisions. 



2. Studies designed to extend our fundamental knowledge of mutation and mutant ef- 

 fects, and to indicate ways in which this knowledge can be used in arriving at improved 

 estimates of radiation damage to be expected from given levels of radiation. 



For the first group of projects there is obvious need for a more nearly adequate defini- 

 tion of the social burden due to genetic damage. This requires estimates of the amount of 

 harm done by various human abnormalities and the determination of the extent to which 

 these are genetic in origin. The latter can be estimated by pedigree analysis, by studies of 

 twins and foster children, and by studies of children of consanguineous marriages. 



Estimates of the extent to which radiation-induced mutation adds to the social burden 

 can be obtained in various ways, among them: further analysis of the descendants of human 

 groups who have for one reason or another been exposed to doses of ionizing radiation much 

 higher than average, and comparison with appropriately chosen controls; studies of mutation 

 rates at specific loci and total rates for broad classes of mutations (e.g., lethals) in mammals 

 of various lengths of life cycle; and studies of fecundity, growth, sex ratio, development, mor- 

 tality, and behavior in the descendants of mammals exposed to ionizing radiation. Such 

 studies should compare chronic and acute radiation dosages, they should include radiation 

 given over a single generation and over successive generations, and they should estimate the 

 effects of differing levels of inbreeding in the exposed population. 



Work has already been done in these areas and some is being extended. For example, 

 the World Health Organization has a special committee at work on the problem of investigat- 

 ing human populations exposed to higher than average levels of ionizing radiation. 



Studies of these kinds, taken together with conventional genetic assumptions and exist- 

 ing information from experimental studies, will permit improved assessments of the genetic 

 risk for different radiation exposures. These, of course, may have to be revised periodically 

 as more knowledge becomes available. 



Investigations of the second type of project, necessarily more long-range in nature and 

 aimed at extension of fundamental knowledge and at possible factors mitigating against radia- 



