Scoring Of Chromosome Aberrations Research Articles

Metaphase-Based Cytogenetic Approach Identifies Radiation-Induced Chromosome and Chromatid Aberrations in Zebrafish Embryos.

Metaphase-based cytogenetic methods based on scoring of chromosome aberrations for the estimation of the radiation dose received provide a powerful approach for evaluating the associated risk upon radiation exposure and form the bulk of our current knowledge of radiation-induced chromosome damages. They mainly rely on inducing quiescent peripheral lymphocytes into proliferation and blocking them at metaphases to quantify the damages at the chromosome level. However, human organs and tissues demonstrate various sensitivity towards radiation and within them, self-proliferating progenitor/stem cells are believed to be the most sensitive populations. The radiation-induced chromosome aberrations in these cells remain largely unknown, especially in the context of an intact living organism. Zebrafish is an ideal animal model for research into this aspect due to their small size and the large quantities of progenitor cells present during the embryonic stages. In this study, we employ a novel metaphase-based cytogenetic approach on zebrafish embryos and demonstrate that chromosome-type and chromatid-type aberrations could be identified in progenitor cells at different cell-cycle stages at the point of radiation exposure. Our work positions zebrafish at the forefront as a useful animal model for studying radiation-induced chromosome structural changes in vivo.

Complex Approach to Evaluating Genotoxicity from Occupational Factors in Coal Mining Industry

The level of cytogenetic damage was analyzed in coal miners (N = 116) and the control sample (N = 169) using an assay for scoring of chromosomal aberrations (CAs) and the DNA comet assay in lymphocytes, as well as the micronucleus test in buccal epithelial cells (MN in BEC). The group of coal miners was characterized by a statistically significantly increase in the main index values of the used test system, compared to the control group. Specifically, the level of chromosomal aberrations in the miner and control groups was 4.69 ± 0.28 and 2.13 ± 0.10%; the proportion of DNA in the comet tail was 4.33 ± 0.38 and 2.16 ± 0.24%; and the micronucleus level was 1.44 ± 0.21 and 0.23 ± 0.12‰, respectively (Р < 0.05). Moreover, in the sample of coal miners, a considerable increase in the levels of additional test indices was observed. For CAs, these parameters included the frequency of single fragments, chromatid-type aberrations, paired fragments, dicentrics without fragments, chromosome exchanges, and chromosome-type aberrations; for the DNA comet assay, these were the comet tail moment and Olive tail moment; for the MN in BEC, the frequencies of binucleated cells, cells with notched nuclei, geminate nuclei, karyorhexis, and apoptotic bodies. Ranking of the results according to major cytogenetic abnormalities made it possible to establish that, in the group of miners, the proportion of individuals with the index values above the background was 68.97% for CAs, 52.13% for the DNA comet assay, and 36.08% for the MN in BEC. The proportion of individuals with cytogenetic damage higher than the background simultaneously in three test systems was 20% of the total sample of miners. To assess the mutagenic effects from occupational factors of coal mining enterprises, it seems reasonable to use a complex of test systems (CA test, DNA comet assay, and MN in BEC).

A NEW METHODOLOGY FOR DIAGNOSIS OF FANCONI ANEMIA BASED ON BIOLOGICAL DOSIMETRY

Fanconi Anemia (FA) is a syndrome associated with chromosomal fragility. Current laboratory tests to diagnose this disease are based on the scoring of chromosomal aberrations induced in peripheral blood lymphocytes by clastogenic chemical agents, mainly: diepoxybutane (DEB) or mitomycin C (MMC). This study evaluated an alternative test for the diagnosis of FA, in which ionizing radiation replaces DEB/MMC. Two groups were studied: normal and DEB-sensitive individuals. From each individual, samples of peripheral blood were irradiated using an electron linear accelerator. Following lymphocyte cultures, and slide preparation, metaphases were scored based on the same methodology for biological dosimetry, according to recommendations of the International Atomic Energy Agency. Our results emphasized a pattern of distribution of dicentrics, fragments, as well as abnormal chromosomal arrangements. The methodology of analysis here proposed permitted to distinguish normal from DEB-sensitive subjects.

A NOVEL BIOLOGICAL DOSIMETRY ASSAY AS A POTENTIAL TOOL FOR TRIAGE DOSE ASSESSMENT IN CASE OF LARGE-SCALE RADIOLOGICAL EMERGENCY

In case of mass radiological emergencies, new strategies involving biological and clinical endpoints are requested for an efficient triage classification of casualties. For this purpose, we developed a novel protocol combining the two most established cytogenetic methods used in biological dosimetry (dicentric and micronucleus assays) into a single one, in order to have a time-saving, inexpensive and potentially automatable instrument to be used for triage purposes in case of large-scale radiological events. This method could be considered as a 'three in one' assay allowing the simultaneous scoring of chromosome aberrations and micronuclei on a single slide, and also enabling to discriminate between metaphases in first and second cell division without the Fluorescence plus Giemsa staining. This method needs further validation through inter-comparisons involving biological dosimetry laboratories, to verify its reproducibility. Moreover, the possibility to apply the already existing software for automation for dicentric and micronucleus assays could be also verified.

Image processing in biodosimetry: A proposal of a generic free software platform.

The scoring of chromosome aberrations is the most reliable biological method for evaluating individual exposure to ionizing radiation. However, microscopic analyses of chromosome human metaphases, generally employed to identify aberrations mainly dicentrics (chromosome with two centromeres), is a laborious task. This method is time consuming and its application in biological dosimetry would be almost impossible in case of a large scale radiation incidents. In this project, a generic software was enhanced for automatic chromosome image processing from a framework originally developed for the Framework V project Simbio, of the European Union for applications in the area of source localization from electroencephalographic signals. The platforms capability is demonstrated by a study comparing automatic segmentation strategies of chromosomes from microscopic images.

'BioQuaRT' project: design of a novel in situ protocol for the simultaneous visualisation of chromosomal aberrations and micronuclei after irradiation at microbeam facilities.

The aim of the 'BioQuaRT' (Biologically weighted Quantities in RadioTherapy) project is to develop measurement techniques for characterising charged particle track structure on different length scales, and to correlate at the cellular level the track structure properties with the biological effects of radiation. This multi-scale approach will allow characterisation of the radiation qualities used in radiotherapy and the related biological effects. Charged-particle microbeam facilities were chosen as the platforms for all radiobiology experiments in the 'BioQuaRT' project, because they allow targeting single cells (or compartments of a cell) with a predefined number of ionising particles and correlating the cell-by-cell induced damage with type and energy of the radiation and with the number of ions per cell. Within this project, a novel in situ protocol was developed for the analysis of the misrepaired and/or unrepaired chromosome damage induced by charged-particle irradiations at the Physikalisch-Technische Bundesanstalt (PTB) ion microbeam facility. Among the cytogenetic biomarkers to detect and estimate radiation-induced DNA damage in radiobiology, chromosomal aberrations and micronuclei were chosen. The characteristics of the PTB irradiation system required the design of a special in situ assay: specific irradiation dishes with a base made from a biofoil 25-µm thick and only 3000-4000 cells seeded and irradiated per dish. This method was developed on Chinese hamster ovary (CHO) cells, one of the most commonly used cell lines in radiobiology in vitro experiments. The present protocol allows the simultaneous scoring of chromosome aberrations and micronuclei on the same irradiated dish. Thanks to its versatility, this method could also be extended to other radiobiological applications besides the single-ion microbeam irradiations.

A new inverse regression model applied to radiation biodosimetry.

Biological dosimetry based on chromosome aberration scoring in peripheral blood lymphocytes enables timely assessment of the ionizing radiation dose absorbed by an individual. Here, new Bayesian-type count data inverse regression methods are introduced for situations where responses are Poisson or two-parameter compound Poisson distributed. Our Poisson models are calculated in a closed form, by means of Hermite and negative binomial (NB) distributions. For compound Poisson responses, complete and simplified models are provided. The simplified models are also expressible in a closed form and involve the use of compound Hermite and compound NB distributions. Three examples of applications are given that demonstrate the usefulness of these methodologies in cytogenetic radiation biodosimetry and in radiotherapy. We provide R and SAS codes which reproduce these examples.

Role of caffeic acid phenethyl ester on mitomycin C induced clastogenesis: analysis of chromosome aberrations, micronucleus, mitotic index and adenosine deaminase activity in vivo

The aim of the present investigation is to determine whether the caffeic acid phenethyl ester (CAPE) in combination with mitomycine-C (MMC) can ameliorate MMC-induced clastogenesis in the bone marrow cells of mice. The scoring of chromosomal aberrations, mitotic activity and micronuclei were undertaken in the current study as markers of clastogenicity. The action of CAPE in adenosine deaminase enzyme (ADA) activities of serum, thymus and spleen were also investigated. The animals were orally administered CAPE alone at the doses 5 or 10mgkgb.wt.(-1) for 5days then sacrificed 24hours after the CAPE administration. MMC was administered to mice either alone at a single dose (2mgkgb.wt.(-1)) by intraperitoneal injection, before or after CAPE treatment. Pre or post - treatment with two doses of CAPE significantly decreased the number of chromosomal aberrations, micronuclei and adapted the mitotic activity reduction in the bone marrow cells of mice induced by MMC when compared with only MMC given group. In addition, combination treatment with MMC caused a significant decrease in the activities of ADA in serum, thymus and spleen. The results of this study showed that ADA activity probably related to high levels of reactive oxygen species. This study concluded that the protective effect of CAPE against MMC clastogenesis resides at least in part, in its antioxidant effects.

Salubrious effects of dexrazoxane against teniposide-induced DNA damage and programmed cell death in murine marrow cells

The intention of the present study was to answer the question whether the catalytic topoisomerase-II inhibitor, dexrazoxane, can be used as a modulator of teniposide-induced DNA damage and programmed cell death (apoptosis) in the bone marrow cells in vivo. The alkaline single cell gel electrophoresis, scoring of chromosomal aberrations, micronuclei and mitotic activity were undertaken in the current study as markers of DNA damage. Apoptosis was analysed by the occurrence of a hypodiploid DNA peak and caspase-3 activity. Oxidative stress marker such as intracellular reactive oxygen species production, lipid peroxidation, reduced and oxidised glutathione were assessed in bone marrow as a possible mechanism underlying this amelioration. Dexrazoxane was neither genotoxic nor apoptogenic in mice at the tested dose. Moreover, for the first time, it has been shown that dexrazoxane affords significant protection against teniposide-induced DNA damage and apoptosis in the bone marrow cells in vivo and effectively suppresses the apoptotic signalling triggered by teniposide. Teniposide induced marked biochemical alterations characteristic of oxidative stress including accumulation of intracellular reactive oxygen species, enhanced lipid peroxidation, accumulation of oxidised glutathione and reduction in the reduced glutathione level. Prior administration of dexrazoxane ahead of teniposide challenge ameliorated these biochemical alterations. It is thus concluded that pretreatment with dexrazoxane attenuates teniposide-induced oxidative stress and subsequent DNA damage and apoptosis in bone marrow cells. Based on our data presented, strategies can be developed to decrease the teniposide-induced DNA damage in normal cells using dexrazoxane. Therefore, dexrazoxane can be a good candidate to decrease the deleterious effects of teniposide in the bone marrow cells of cancer patients treated with teniposide.

The impact of quercetin on cisplatin-induced clastogenesis and apoptosis in murine marrow cells

The aim of the present investigation is to determine whether the quercetin in combination with cisplatin can ameliorate cisplatin-induced clastogenesis and apoptosis in the bone marrow cells of mice. The scoring of chromosomal aberrations, micronuclei and mitotic activity were undertaken in the current study as markers of clastogenicity. Apoptosis was analysed by the Annexin V-propidium iodide assay and the occurrence of a hypodiploid DNA peak. Oxidative stress markers such as bone marrow lipid peroxidation and reduced glutathione were assessed as a possible mechanism underlying this amelioration. Quercetin was neither clastogenic nor apoptogenic in mice at doses equivalent to 50 or 100 mg/kg for 2 days. Pre-treatment of mice with quercetin significantly reduced cisplatin-induced clastogenesis and apoptosis in the bone marrow cells and these effects were dose and time dependent. Prior administration of quercetin ahead of cisplatin challenge ameliorated oxidative stress markers. Overall, this study provides for the first time that quercetin has a protective role in the abatement of cisplatin-induced clastogenesis and apoptosis in the bone marrow cells of mice that resides, at least in part, in its antioxidant effects. Therefore, quercetin can be a good candidate to decrease the deleterious effects of cisplatin in the bone marrow cells of cancer patients treated with this drug.

The influence of x-ray contrast agents in computed tomography on the induction of dicentrics and γ-H2AX foci in lymphocytes of human blood samples

The aim of this study was to investigate and quantify two biomarkers for radiation exposure (dicentrics and γ-H2AX foci) in human lymphocytes after CT scans in the presence of an iodinated contrast agent. Blood samples from a healthy donor were exposed to CT scans in the absence or presence of iotrolan 300 at iodine concentrations of 5 or 50 mg ml−1 blood. The samples were exposed to 0.025, 0.05, 0.1 and 1 Gy in a tissue equivalent body phantom. Chromosome aberration scoring and automated microscopic analysis of γ-H2AX foci were performed in parts of the same samples. The theoretical physical dose enhancement factor (DEF) was calculated on the basis of the mass energy-absorption coefficients of iodine and blood and the photon energy spectrum of the CT tube. No significant differences in the yields of dicentrics and γ-H2AX foci were observed in the absence or presence of 5 mg iodine ml−1 blood up to 0.1 Gy, whereas at 1 Gy the yields were elevated for both biomarkers. At an iodine concentration of 50 mg ml−1 serving as a positive control, a biological DEF of 9.5 ± 1.4 and 2.3 ± 0.5 was determined for dicentrics and γ-H2AX foci, respectively. A physical DEF of 1.56 and 6.30 was calculated for 5 and 50 mg iodine ml−1, respectively. Thus, it can be concluded that in the diagnostic dose range (radiation and contrast dose), no relevant biological dose-enhancing effect could be detected, whereas a clear biological dose-enhancing effect could be found for a contrast dose well outside the diagnostic CT range for the complete radiation dose range with both methods.

Atypical retinoids ST1926 and CD437 are S-phase-specific agents causing DNA double-strand breaks: significance for the cytotoxic and antiproliferative activity

Retinoid-related molecules (RRM) are novel agents with tumor-selective cytotoxic/antiproliferative activity, a different mechanism of action from classic retinoids and no cross-resistance with other chemotherapeutics. ST1926 and CD437 are prototypic RRMs, with the former currently undergoing phase I clinical trials. We show here that ST1926, CD437, and active congeners cause DNA damage. Cellular and subcellular COMET assays, H2AX phosphorylation (gamma-H2AX), and scoring of chromosome aberrations indicate that active RRMs produce DNA double-strand breaks (DSB) and chromosomal lesions in NB4, an acute myeloid leukemia (AML) cell line characterized by high sensitivity to RRMs. There is a direct quantitative correlation between the levels of DSBs and the cytotoxic/antiproliferative effects induced by RRMs. NB4.437r blasts, which are selectively resistant to RRMs, do not show any sign of DNA damage after treatment with ST1926, CD437, and analogues. DNA damage is the major mechanism underlying the antileukemic activity of RRMs in NB4 and other AML cell lines. In accordance with the S-phase specificity of the cytotoxic and antiproliferative responses of AML cells to RRMs, increases in DSBs are maximal during the S phase of the cell cycle. Induction of DSBs precedes inhibition of DNA replication and is associated with rapid activation of ataxia telangectasia mutated, ataxia telangectasia RAD3-related, and DNA-dependent protein kinases with subsequent stimulation of the p38 mitogen-activated protein kinase. Inhibition of ataxia telangectasia mutated and DNA-dependent protein kinases reduces phosphorylation of H2AX. Cells defective for homologous recombination are particularly sensitive to ST1926, indicating that this process is important for the protection of cells from the RRM-dependent DNA damage and cytotoxicity.

Nutritional supplementation with antioxidants decreases chromosomal damage in humans.

In order to investigate the effects of antioxidant supplementation on chromosome damage, a 3 month antioxidant supplementation trial was conducted on groups of 28 myocardial infarction survivors and 57 rural controls, all male. The supplement consisted of vitamin C (100 mg/day), vitamin E (100 mg/day), beta-carotene (6 mg/day) and selenium (50 microg/day). Dietary antioxidants in plasma were measured, as well as the ferric reducing ability of plasma (a measure of total plasma antioxidant status) and the concentration of malondialdehyde as an indicator of oxidative stress. Lymphocytes collected at the beginning and end of the supplementation period were stimulated to proliferate and metaphases accumulated for scoring of chromosome aberrations: per cent aberrant cells and chromatid and chromosome breaks. Supplementation with antioxidants was associated with a decrease in the percentage of cells with chromosome aberrations in the group of rural controls (0.63% before compared with 0.27% after supplementation; P = 0.03). The largest effect of supplementation was seen in smokers in this group (0.12% aberrant cells in supplemented compared with 0.81% in placebo group; P > 0.001). The results support the hypothesis that antioxidants decrease genetic damage.

Trends in biological dosimetry: an overview

Biological dosimetry (biodosimetry) is based on investigations of induced biological effects (biomarkers) in order to correlate them with radiation dose. Among the indicators employed in biodosimetry, scoring of chromosome aberrations is the most reliable method to quantify individual exposure to ionizing radiation. The technique, applied to circulating lymphocytes, has been developed into a routine procedure to evaluate the dose in the case of real or suspected accidental exposure. Considering the radiosensitivity of lymphocytes in vitro and in vivo as being the same, the dose effect relationship obtained after in vitro irradiation of blood has been widely used, with medico-legal value, for evaluating individual radiation exposure. This report presents an overview of strengths, limitations and perspectives on biodosimetry.

Validation de la dosimétrie biologique chez des patients conditionnés par irradiation corporelle totale : étude cytogénétique conventionnelle et hybridation in situ (FISH)

Purpose. – Validation of biological dosimetry versus physical dosimetry in malignant haemopathy patients conditioned by total body irradiation (TBI) before bone marrow transplantation (BMT). Patients and methods. – The scoring of chromosomal aberrations in peripheral lymphocytes irradiated in vivo was used to perform the biological dosimetry. The data were compared to those obtained with healthy volunteers' total blood exposed to in vitro irradiation with linear accelerator doses (0.2, 0.5, 0.75, 1, 2, 3, 4 and 5 Gy) for dose-response curves. In experimental animal models, can in vivo and in vitro responses be considered as being the same? All the published human data are based on retrospective dose evaluation with very large uncertainties on the dose precisely delivered to the subject. TBI before BMT was taken as a model where the dose calculation results from the physical method, with homogeneous beam and dose delivered precisely along the entire organism. In vivo response allows us to validate biological dosimetry in 15 adult patients (female + male), before (D = 0 Gy) and after the first fraction of 1.8 Gy, delivered by a linear accelerator (18 MV, dose-rate of 15.8 cGy/min –1). Two methods, conventional cytogenetics (CCG) and fluorescent in situ hybridization (FISH painting) of chromosome 4 were respectively used to analyze the unstable chromosome aberrations and stable chromosome aberrations. Results. – Healthy volunteer lymphocytes, before irradiation, yielded 0.1% dicentrics and 0.3% translocations of chromosome 4, with 2.5% for the whole genome. Patients before irradiation had 2% dicentrics and 11.48% chromosome 4 translocations for the whole genome. In the 15 patients, for a physical dose of 1.8 Gy, the evaluated biological dose was 1.93 Gy (95% CI: 1.85–2.05 Gy) with conventional cytogenetics and 2.06 Gy (95% CI: 1.75–2.15 Gy) with FISH. Conclusion. – These results, in which the biologically estimated dose is in complete agreement with the dose calculated by physical dosimetry in the homogeneous irradiation model, suggest the validation of biological dosimetry in TBI conditioning.

Bleomycin-induced chromosome aberrations in head and neck cancer patients analyzed by classical cytogenetics and FISH

Individual sensitivity to mutagens has been considered to play an important role in head-and-neck squamous cells carcinoma (HNSCC) development. The bleomycin test was introduced for establishing constitutional susceptibility to mutagens (T.C. Hsu, D.A. Johnston, L.M. Cherry, D. Ramkisson, S.P. Schantz, J.M. Jessup, R.J. Winn, L. Shirley, C. Furlong, Sensitivity to genotoxic effects of bleomycin in humans: possible relationship to environmental carcinogenesis, Int. J. Cancer 43 (1989) 403–409). Its criteria are based on scoring of chromosome aberrations (CAs, mainly breaks) in Giemsa-stained chromosomes. Fluorescence in situ hybridization (FISH) offers an easy method for analysis of translocations, acentric fragments and dicentrics. In the present study FISH was applied in the analysis of bleomycin-induced CAs of the HNSCC patients and controls. The results proved that FISH is a complementary method to the classical staining in monitoring of bleomycin-induced CAs.

The Use of Chromosomal Aberrations in Human Lymphocytes for Biological Dosimetry

The scoring of chromosomal aberrations in human lymphocytes provides the most sensitive method known for biological dosimetry. By scoring dicentrics in the full genome of 500 cells, average whole-body doses of about 0.1 Gy of X or gamma rays may be detected and higher doses estimated. Acute doses above about 0.2 Gy can be estimated more accurately than similar chronic doses. For radiations of higher LET, for example those encountered in the space environment, the limits of detection in grays are lower. However, expressed in sieverts, the limits of detection are more nearly independent of radiation quality. This suggests for exposure to space radiations that it may be possible to convert the yield of aberrations directly to an average whole-body dose in sieverts, which can be used as an estimate of effective dose. The scoring of translocations involving about 20% of the genome in 1000 cells using fluorescence in situ hybridization painting techniques results in a reduced sensitivity at low doses so that acute X-ray doses of about 0.3 Gy and chronic doses of about 0.4 Gy are at the limit of measurement. Better sensitivity can be achieved by scoring more cells or by using more chromosomes in color combinations, but a final limit to these approaches exists because of the higher level of spontaneous translocations than dicentrics in cells of unirradiated persons.

Prediction of human cell radiosensitivity: Comparison of clonogenic assay with chromosome aberrations scored using premature chromosome condensation with fluorescence in situ hybridization

Purpose : The purpose of the present investigation was to determine whether chromosome aberrations scored by premature chromosome condensation (PCC) and fluorescence in situ hybridization (FISH) can predict the radio sensitivity of human cell lines, thereby providing a possible means of assessing the in situ radiosensitivity of normal tissues and the radiocurability of individual human cancers. Methods and Materials : We used four cells lines of different radiosensitivity: normal human fibroblasts (AG1522), ataxia-telangiectasia fibroblasts (AT2052), a human fibrosarcoma cell line (HT1080), and a human melanoma cell line (melanoma 903). These were irradiated in plateau phase with a range of doses and assessed both for clonogenic cell survival and for aberrations in a single chromosome (number 4) immediately after, and 24 h after irradiation. Results : The initial number of breaks in chromosome 4 was proportional to irradiation dose and was identical for all the different human cell lines, irrespective of radiosensitivity. On the other hand, the number of chromosome 4 breaks remaining 24 h after irradiation reflected the radiosensitivity of the cells such that the relationship between residual chromosome aberrations and cell survival was the same for the different cell lines. Conclusions : These results suggest that the scoring of chromosome aberrations in interphase using FISH with PCC holds considerable promise for predicting the radiosensitivity of normal and tumor tissues in situ.

Robot system for preparing lymphocyte chromosome.

Towards the automatization of the scoring of chromosome aberrations in radiation dosimetry with the emphasis on the improvement of biological preparations, the conventional culture and harvesting method was modified. Based on this modified method, a culture and harvest robotic system (CHROSY) for system (CHROSY) for preparing lymphocyte chromosome was developed. The targeted points of the modification are as in the following. 1. Starting culture with purified lymphocytes in a fixed cell number. 2. Avoiding the loss of cells in changing the liquids following centrifugalization. 3. Keeping the quantity of the liquids to be applied to the treatments of cells fixed. 4. Building a system even a beginner can handle. System features are as follows. 1. Operation system: Handling robot having 5 degrees of freedom; a rotator incubator with an automatic sliding door; units for setting and removing pipette tips; a centrifuge equipped with a position adjuster and an automatic sliding door; two aluminum block baths; two nozzles as pipettes and aspirators connected to air pumps; a capping unit with a nozzle for CO2 gas; a compressor; and an air manipulated syringe. 2. Control system: NEC PC-9801RX21 with CRT; and program written in Basic and Assembly languages on MS-DOS. It took this system 2 hours and 25 minutes to harvest 2 cultures. A fairly good chromosome slide was made from the sample harvested by CHROSY automatically.

Labeling of human centromeres using an alphoid DNA consensus sequence: application to the scoring of chromosome aberrations

Precise identification of centromeres is required for accurate scoring of asymmetrical chromosome aberrations, such as dicentrics. The centromeric regions of all human chromosomes can be labeled by in situ hybridization of a 30 nucleotide oligomer having the sequence of a conserved region of an alphoid DNA consensus sequence. Fluorescent detection of the hybridized probe allows rapid identification of centromeres and accurate scoring of dicentrics, multicentrics, acentric fragments, and the centromeric content of ring chromosomes. This procedure provides a novel approach for scoring these complex chromosome aberrations, particularly damage induced by radiation or radiomimetic agents.