Seymour Abrahamson

James F. Crow: His Life in Public Service

The readers of this journal may well be aware of Professor Crow’s scientific achievements and his role as the editor of Perspectives. In addition, for many thousands of students at the University of Wisconsin over many generations, James F. Crow was one of the most memorable teachers at both the undergraduate and graduate levels. What is less known is his major role in public service where he served as chair of many important committees for the National Academy of Sciences, the National Institutes of Health, the National Institutes of Justice as well as various international programs. In all of these efforts, Professor Crow has left a lasting impact.

Risk of stillbirth in offspring of men exposed to ionising radiation.

Radiation genetic risk models are employed to predict the frequency of radiation-related stillbirths to partners of occupationally exposed male workers, using the incidence data recently reported by Parker et al from an epidemiological study of Cumbrian births. Expanding on previously developed conservative risk estimates suggests that, of the 130 observed stillbirths to partners of male radiation workers, 0.3 cases would be attributable to paternal preconceptional irradiation, in contrast to the 17.5 (95% confidence interval: 3.1 to 31.9) cases predicted by Parker et al from their preferred dose-response model. The incompatibility of the results reported by Parker et al with those from other investigations, both epidemiological and experimental, and the inability of the study to consider a number of factors which might affect stillbirth rates, particularly those relating to the mother, make it difficult to accept that paternal irradiation received occupationally could have contributed to a detectable increase in stillbirths.

The Shapes of the Radiation Dose-Mutation Response Curves in Drosophila: Mechanisms and Implications

The major thesis we wish to make in this presentation is that radiation induced mutations, namely sex-linked recessive lethals in Drosophila and forward mutations at specific loci in Drosophila, mammals and lower eucaryotes, are the result of two sub-lesions or hits, induced by either single ionization tracks or by the interaction of two independent tracks for low LET radiations, when the dose is delivered in an acute fashion. This statement formally reduces to the well recognized linear quadratic expression: Y = C + αD + βD2 where C is the spontaneous frequency of events scored and α and β represent the coefficients of the dose. In practice, the curve is more complex because saturation occurs at high doses. This linear-quadratic relationship is most often applied to the yield of gross chromosome aberrations in plant and animal systems and was first demonstrated by Sax (1940). Lea (1955) and subsequently Neary (1965) and Kellerer and Rossi (1972) have developed the biophysical and microdosimetric framework for the empirically derived dose-response relationship.

Risk Estimate for Genetic Effects

It is not my intention to reinvent the wheel in this presentation, but perhaps I can straighten a few spokes, here and there. I have been a member of both the National Academy’s BEIR and CCEM committees concerning risk from ionizing radiation (National Research Council, 1972, 1980) and environmental chemical mutagens (National Research Council, 1983) and will provide a general summary of approaches used in their reports. In the case of radiation, Bender, Denniston, Schull and myself have recently prepared a detailed risk report for the Nuclear Regulatory Commission’s updated reactor safety study and so I also will incorporate major elements of that unpublished report into this discussion.

The modification of X-ray induced chromosome changes with anoxia in different oocyte stages of Drosophila melanogaster

Abstract The effect of postirradiation treatment with anoxia on the detachment of attached-X chromosomes induced by X-rays in stage-7 and stage-1 4 oocytes was studied. Anoxia produced a highly significant increase ( P 4 oocytes indicate that anoxic posttreatments produce a significant increase ( P = 0.005) in the frequency of detachments. Thus anoxia has an effect on both stage-7 and stage-1 4 oocytes. It is suggested that anoxia keeps breaks open longher than air and also allows for enhanced movement of broken chromosome ends which leads to an increase in the rearrangement frequency. It is expected that this mechanism would be more effective in stge-7 cells, where any delay in rejoining and added movement will greatly increase the chance for rearrangement where normally a short time exists for chromosome movement prior to rejoining. Stage-1 4 oocytes, where broken chromosomes remain unrestituted until after fertilization and thus have a chance for normal chromosome movement over a period of time, would not be expected to show as great a response to additional movement.

Comparative Mutagenicity of N-Methyl-N′-Nitro-N-Nitrosoguanidine (MNNG) and ICR-170

N-Methyl-N′-nitro-n-nitrosoguanidine (CAS No. 70-25-7) is a widely used laboratory mutagen and carcinogen known by a number of abbreviations, now most commonly MNNG. It has been applied to a wide array of organisms from prokaryotes through mammals and has been clearly demonstrated to produce a spectrum of genetic alterations in nearly all test systems, with some putative exceptions to be discussed below.