35 25).0) Notwo-hit aberrations were found ia the unexposed group, but both groups had at unusual number of accatric fragments, the cause of which is not known, Paradoxically, Kangelap people with the lower exposure had more aberrations than hose with the higher expesure, These studies indicate that a small but significant number of chromosome aberrations persisted in bluod lymphocytes in sone Marshallese as late as 10 vears afler exposure. The results are consistent with these of sunilar studics on the exposed Japanese fishermen’? on victins of other radiation acci- dents.and on Japanese bomb survivors. 74 2, Somatic Mutations bn F971, stadies® were made of the frequency of amine acid substitution in the hemoglobin of the Marshallese on bloodsatiples sent to Qak Ridge.?4 Since there is ne coded isoleucine’? in adult bu- nan hemoglobin A, its presence must be due to errors 12 transcription of translation or to somatic mutauons arising during DNA replication. Errors in Lranscription, which eccur infrequently, form altered mRNA URNA, and FRNA; they change the coding in the mRNA and may reduce the fidelity of the RNA with regard to both the kind of annine acid it accepts and the mRNA codons it recognizes. Ercons iu translation’? arise through the attachinent of wrong amino acids to tRNA (auininaacy! synthetase errors) and the liuprecise recognition of mRNA codons by RNA anticodons (Iranslatonal variation), Somatic mutavous result fron mistakes in replication of DNAS muiny single: Figure 2h. Teo-hit chromescue aber aGoos in capiecd Marshallese. Pop: arrow peanuts to chcestrie bore: bette: irtase poats toe rans bore, 20) and Bo uneaposed Rougelap people.* ChiroInasome aberrauens were noted in 2b of the exposed and ino af the unexposed Marshallese, but the exposed group had a number of two break abcrrativons (represented by dicentric cliramasomes, . Dase-substitution mutations change nanindeucine inte ssicucine codans,* and the resuliing mutant cells could have hemoglobin wR NA with isoleucine codons, For this reason, an inerease i the isoleucine content of hemoglobin A would be expected in hunins exposed te agents causing base- substitution mutations, Possibly radiation may cause base-subsiituiion autations in human somatic cells, but this has never been established. Theisoleucine content of the hemoglobin A was determined in bload frou Vb ex paused Marshallese und 12 unexposed, The frequeney of isoleucine substitution foradher amine acids in hemoglobin was calculated by dividing the nanumoles of iso- leucine by the total nanomoles of all other amino transbocations, anda ring form) that are thoughe to be awsaciated with radiation exposure (Figure acids in cach sample. Vhe frequencies are listed in Table 21, The analees were dene by Des TE Cisco, New England Deaconess Plaapital, and RON, Caaareh BNE. *Therse studios were done by Ors RV. Popp. GOPLire hy and FG Haat ok Kadye Notional | aboeatory,