Chromosomes in primary tumour cells derived from a squamous cell carcinoma of the gingival mucosa were analysed. The ploidy of individual chromosomes and the frequencies of reciprocal translocations in unirradiated and irradiated cells were assessed by the method of fluorescence in situ hybridization. Hybridization probes for whole chromosomes 1, 2, 3, 4, 9 and 12 were used. The analysis was carried out in early (1st-3rd) passage cells and for comparison, in late (25th-30th) passage cells. A radiation-induced polyploidy of all analysed chromosomes was observed in irradiated (D = 4 Gy) early as well as late passage cells, with the exception of chromosome 4 in late passage cells. Ploidy of chromosomes 1 and 4 was studied at lower doses (1-3 Gy), too. Polyploidy was observed for doses >2 Gy. Some of the analysed chromosomes showed a high 'spontaneous' translocation frequency in both types of cells. The frequencies of radiation-induced translocations were similar in early and late cells and these frequencies were not always proportional to the length of the chromosomes studied. The radiosensitivity of individual chromosomes was not correlated with the level of spontaneous translocation frequency.

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