12 BIOLOGICAL EFFECTS OF ATOMIC RADIATION 



very likely that there are such selective advantages of heterozygotes for deleterious mutants 

 over their "normal" homozygous counterparts. Incomplete dominance and overdominance 

 should be studied for mutant genes produced in a variety of ways — by "natural" mutation, 

 by artificially applied radiation, and by treatment with other mutagenic agents. 



Some mutant genes produce large effects that are easily identified; many more produce 

 smaller effects that are often difficult to analyze. We need more information on the frequency 

 and properties of this latter type. It may be hoped that new methods of study applicable to 

 man will be developed; but it is also desirable that the rather laborious (and sometimes dis- 

 couragingly inconclusive) methods now available be further exploited, and that all methods 

 be applied as widely and as rapidly as possible. 



Mutant genes also differ in the type of character involved, and the techniques necessary 

 for their study are correspondingly varied. Some of the types of characters that are important 

 from a social point of view are especially difficult to analyze — those having to do with mental 

 properties, for example. It is important that twin studies be pursued here, and that other 

 methods of approach be developed. Perhaps additional progress could be made by the study 

 of behavior patterns in laboratory mammals; these might at least give some indication of the 

 relative frequency of mutations in some components of the mental makeup of individuals. 



Estimates of damage due to mutation will be affected by the frequency of "pleiotropy" 

 (multiple phenotypic effects of single genes), of "synergism" (greater than additive coopera- 

 tion of genes at different loci in producing a given effect), and of cases in which given 

 mutant effects are simulated by mutations at other loci or by environmental effects. We need 

 evidence — especially from man and other mammals — on the relative frequencies of inter- 

 relations of these and similar kinds among genes (especially radiation-induced mutant genes) 

 and among characters. 



Almost any mutant gene varies in its effects on different individuals that bear it; at times 

 this variability may be extreme, ranging from no detectable effect at all up to extreme mal- 

 formations. Such variations are sometimes due to detectable genetic or environmental causes; 

 in other cases, they have the appearance of occurring at random. The frequency and charac- 

 teristics of the phenomenon need study — again especially in mammals — since they will be 

 important in any attempt to make quantitative estimates. 



3. The Behavior of Genes in Populations 



If we knew the quantitative relations between mutation frequency and radiation dosage, 

 and also had good estimates of the amount of damage to an individual resulting from each 

 mutant gene produced, we still would not have solved one of the problems presented to us, 

 namely, what happens to these genes when they are introduced into the population, and also 

 what happens to the population. 



This type of problem requires a knowledge, not now available, of the breeding struc- 

 ture of human populations. We need to know such things as the degree of inbreeding (fre- 

 quency of marriages between first cousins and more remote relatives) and its relation, as well 

 as that of other factors, to number of descendants. Some of the needed kinds of information 

 can be extracted from existing vital statistics and hospital and other medical records; it is to 

 be hoped that methods of collecting and filing such statistics can be instituted that would make 

 them much more useful for this purpose. In this connection it may be pointed out that one of 

 the unique features of man as a genetic organism is that pedigrees are recorded in one way or 



