196 



of Thomas M. Rivers (chairman), 

 George W. Beadle, Detlev W. Bronk, 

 Austin Brues, George M. Lyon, C. P. 

 Rhoads, Shields Warren, Stafford L. 

 Warren, George H. Whipple, and Ray- 

 mond E. Zirkle. 



The potential genetic effects of the 

 atomic bomb were apparent to all inter- 

 ested students from the day the first 

 bomb was dropped — in fact, to some, 

 well before that time. A consideration of 

 genetic studies was one facet of the work 

 of the Atomic Bomb Casualty Commis- 

 sion, and a section of its January 1947 

 report was devoted to this subject. This 

 phase of the work was to a large extent 

 the responsibilit)^ of Lt. James V. Neel. 



On June 24, 1947, the Committee on 

 Atomic Casualties arranged a conference 

 on the potential genetic effects of the 

 atomic bombs. At this meeting, which 

 was attended by George W. Beadle 

 (chairman), Donald R. Charles, Charles 

 H. Danforth, Herman J. Muller, Lau- 

 rence H. Snyder, and Lt. Neel, the latter 

 submitted a report of preliminary genetic 

 studies, based on his observations in Japan 

 during the preceding six months. Follow- 

 ing a thorough appraisal of the problem, 

 the conference voted to recommend to 

 the Committee on Atomic Casualties that 

 a program be undertaken in Japan along 

 the lines sketched out in the Neel report. 

 This recommendation was accepted at a 

 meeting of the Committee on June 26, 

 1947. The conference also recommended 

 that a statement be prepared, briefly sum- 

 marizing the current status of the prob- 

 lem. This statement follows. 



Whether the atomic bombs 

 dropped on Hiroshima and Nagasaki 

 will have detectable genetic effects on 

 the Japanese is a question of wide- 

 spread interest. The purpose of the 

 present note is to show briefly that ( 1 ) 

 many difficulties beset any attempt to 

 obtain a valid answer to this question 

 and (2) even after a long-term study, 

 such as that outlined below, it still may 

 not be possible to determine just how 

 much genetic damage was done at 

 Hiroshima and Nagasaki. 



GENETICS CONFERENCE 



This memorandum is essentially a 

 partial summary of the material pre- 

 sented by Lt. James V. Neel at the 

 meeting of the Conference on Ge- 

 netics convened by the Committee on 

 Atomic Casualties of the National Re- 

 search Council on June 24, 1947, but 

 with certain additional considerations 

 which grew out of the deliberations of 

 the Conference. 



It must first be recognized that, inas- 

 much as the majority of mutations oc- 

 curring in animals are recessive, only 

 the relatively small proportion of mu- 

 tations which are dominants may be 

 expected to show effects in the first 

 postbomb generation. The potential 

 range in their effects is very wide. 

 Dominant mutations with large, clear- 

 cut manifestations can be expected to 

 be much rarer than those with smaller, 

 but possibly quite significant, effects 

 on bodily dimensions, life span, etc. 

 But the detection of these latter is a 

 matter of great difficulty with present 

 techniques. For practical considerations 

 investigation will have to be concen- 

 trated chiefly on the class with such 

 large effects as may lead to stillbirths, 

 to live births with gross external ab- 

 normality, or to internal defects caus- 

 ing death or serious illness in infancy. 



Since there is no general agreement 

 as to what proportion of cases of ab- 

 normal fetal development is genet- 

 ically determined, and what propor- 

 tion is due to nongenetic factors, an 

 increased incidence of morphologi- 

 cally abnormal fetuses following irra- 

 diation may not be used as an index 

 of the frequency of genetic change 

 until the nongenetic effects of this 

 irradiation on the reproductive history^ 

 of the mother have been determined. 

 This point will be very difficult to 

 evaluate. 



It is obvious that in this case the 

 approach to the problem of genetic 

 effects is the statistical one. It is un- 



