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Cytological investigation of tiood . s31~.;1,zi drn:.n 3 x r k g tkz 1961 medical exanination of the ne;. involvcd b, zkie 1-12 critical it y z ber ratio mother thzn the ex-pctec Low frscyencies 2: chroziatid a5erratl;ns divide inthe assay system used ETE ell zrs-chrcraosone-replication, the chrorratid zberrations must arise during the brief culturing in vitro, and not Probably the abnomai counts seen i n control nate rial also arise in vitro, since most abnomal r,u;7lbzrs are beio-d then or ral digloid number, instead of distributed both abcve an6 belox it, as would probably be the z2se abno,mal chronosome number was somewhat higher than t h a t observed i n the 2revious sam2les. Since the excess T ~ ~ slargely of c e l l s with counts lover than 2x1 = 46, the increase i s probably caused by an increase in cell breakage during fixation a15 slide preparation. Such an increase was not observed, however, inc cz tro l x atc rial fixed at about the same the. Tle new sqles from the irradiated men continue t o shov changes i n both Sone changes in their frequencies have been seen,chronosome nmber and form. however. In particular, both rin g- _and minute chroxosomes appear less freGuently
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inthe new sanples . Dicentric chrcxosoms vere secn i n the new sarcples, but the frequency i n one individual ( " C " )is nuch lovw than that seen inthe earlier sample. Xhile it is difficult to establish the statistical significance of such changes in sz T les of this size, $he results of the sresent exaxination, conpared with those of the prev ims one, strGngly su;gest that the frecpezcy of ring, di centric, and rninute chron;oscr,es i s decrezsing with tim i n these men. A detailed kar jot fi ic exazi?&ion of cells fro3the 1961 blood s aq les has been a2proximately one-nalf completed at t h e present tine. karyotype analyses, the presence of aberrations (such as peri centric inversions and symnetrical translocations) that are othe,mise cot visible can be detected. From the analyses completed, it appears that the frequency of these aberrations has not decreased in the year since the last examination. This finding is not unexpected, since these aberrations are probably not selected against as are the di centric s and rings, whicn can be lost through mechanical difficulties eccountered during mitosis. I n many kz ryo t ne analyses indistinguishable abnormal chromosomes were seen in different cells front he same individual. In summary, the present findings suggest that the expected gradual loss of "gross" aberrations, such as rings and dicentrics, from the hematopoietic cell populations of the irradiated men is in fact occurring. On the other hand, aberrations such as peri centric inversions and symmetrical translocations, seem t o be maintaining about the same frequency seen in the earlier s mp les.
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"Gross" aberrations in the peripheral leukocytes of from blood smples dram i n November, 1961 Cells Chromosoze aberrations Abnormal Cells with Carorat i d cells Subject Scored 2n = 46 Aberrztions Minutes Rings Dicentrics Other ( % I f *Karyotypic abnormalities such as abnormal centromere position or abnormal length that were obvious without formal karyotype analysis.
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Status xeport - Varch 1, 1562 Cytological investigation of X ood s aq les draxn during tne 1961 medical exanination of the men involved inthe Y-12 critical it y Scoring of chromosome aberrations i n the blood s&?ples drawn i n November, 1961 fron the eight Zen iwol-zed in the critical it y accident of June, 1958, has been coapleted. compared with tne published infornation forsa ~ $ l e sdrawn i n NoveraSer, 1950. Tnz results ap?ear inthe Table, which rny be Control mter i zl frm ur irradiate a iadividvals conti nils to show no r xi j or aberrations other than the 3jcoecteb low ' f r ? ~ u en cie sof cnromatid aberrations and counts of other than 2n = L 6 (both about 2%). Since t h e leukocytes t h a t divide in the assay systen used are all pre-chroaosome-replication,the chroxatid aberrations must arise during the brief culturing --in vitro, and not . Probably the zbnormal counts seen i n control rnaterial also arise in vitro, since most abnoraal nuxbers are Selow the normal diploid number, instead of distributed both abclve &IC: belod it, as would probably 3sthe case if they occurred i n vivo. abnormal chromosome number was somewhat higher than that observed inthe previous samples. Since the excess was largely of cells with counts lower than 2n = 46, the increase i s probably caused by ar, increzse in cell breakage during fixation and s l i d e preparation. Such an increase was not observed, however, in control material fixed a t about the sane time. The new swles from the irradiated men continue t o shox changes i n both Some changes in their frequencies have been seen,chronosome number and form. however. In particular, both ring and minute chromosomes appear less frequently
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inthe new s mp les. the frequency i n one individual ("C") i s much lover than that seen inthe earlier sample. Yhile it is d iT fi cult to establish the statistical significance of such changes insa - iles of this size,the results of the pre smt exaxinstion, compared with those of the previous one, strongly suggest that the frequency of ring, di centric, and minute chronosones i s decreasing with tirne i n these men. A detailed karyotypic exmination of cells from the 1961 blood s aq les has been approximately one-nalf completed at t h e present time. karyotype analyses, the presence of aberrations (such as peri centric inversions and symmetrical translocation s) that are otherwise not visible can be detected. From the analyses completed, it a?pears that the frequency of tbese aberrations has not decreased inthe year since the last esamination. This finding is not unexpected, since these aberrations are probably not selected against as are the di centric s and rings, vhich can be lost through mechanical difficulties encountered during mitosis. I n many karyotype analyses indistinzuishable abnormal chromosomes were seen h different cells from the s me individual. In summary, the present findings suggest that the eq ec ted gradual loss of "gross" aberrations, such as rings add i centric s, from the hematopoietic cell populations of the irradiated men is in fact occurring. On the other hand, aberrations such as peri centric inversions and symmetrical translocations, seem t o be maintaining about the s me frequency seen in the earlier s mp les.
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"Gross" aberrations in the peripheral leukocytes of Cells Chromosome aberrations Abnom2 Cells with ChroTat id cells *Subject Scored 2n = 46 Aberrations Minutes Rings Dicentrics Other ($1 *Karyotypic abnormalities such as abnormal centromere position or abnormal length t h a t were obvious without formal karyotype analysis.