Exchange aberrations among 11 chromosomes of human lymphocytes induced by gamma-rays

Purpose: To detect the frequencies of inter-changes among 11 chromosomes in lymphocytes irradiated with gamma -rays and to find out whether these freq uencies reflect the proximity of some of these chromosomes within the inter phase nucleus. Material and methods: Exchange aberrations were detected in the first mitos is after irradiation of human lymphocytes with 3 and 5 Gy gamma -rays of` C o-60. Two-colour repeated FISH with two differently chemically modified pro bes in each hybridization was applied. The microscope stage positions of ea ch mitosis were recorded after the first hybridization and used for the aut omatic scanning of images after all successive experiments. Five images wer e obtained for each mitosis differing in visualized pairs of chromosomes. C omparing these images, exchanges among 10 chromosomes could be detected. Pa inting of the p arm of chromosome 21 with the painting probe for chromosome 22 also made it possible to detect exchanges of this chromosome with other chromosomes of the selected group. Results: Frequencies of exchange aberrations induced in chromosomes of the selected group as well as interchanges between many pairs of chromosomes of this group were roughly proportional to the DNA content of chromosomes. Hi gher frequencies of interchanges than expected according to the model of li near proportionality were found between several chromosomes involved in tra nslocations frequent in different subtypes of leukaemia. Conclusions: Frequencies of interchanges among 11 chromosomes of human lymp hocytes induced by gamma -rays do not indicate as clearly as fast neutrons the non-random arrangement of chromosomes in the cell nucleus. The interact ion of a large number of chromosomes in exchange aberrations suggests that the chromatirl in the territory of one chromosome is accessible for several other chromosomes.