Abstract: Purpose : To investigate whether delayed genetic instability is associated with specific chromosomal alterations , this would facilitate the identification of genetic or epigenetic factors that cause delayed instability , and to investigate whether clones which exhibit increased f requencies of delayed int rachromosomal recombination also exhibit increased f requencies of delayed generation of chromosomal aberration. Methods : The pulsed field gel elect rophoresis methods was used to investigate the delayed genetic instability induced byγ2irradiation till 58th generations. Results : Average f requency of recombinations in Rsy - 112 derived f rom unirradiated cells was 3. 5 ×10 - 4 , ranging f rom 2. 7 ×10 - 4 to 4. 6 ×10 - 4 ; all the other clones of Rsy - 112 and HFD which were derived f rom the cells irradiated with doses between 0. 4 kGy～4. 0 kGy were 5. 9 ×10 - 4 and 19. 4 ×10 - 4 , ranging f rom 2. 8 ×10 - 4 to 11. 7 ×10 - 4 and 3. 9 ×10 - 4 to 35. 3 ×10 - 4 , respectively. Conclusion : ①γ2irradiation could lead to a process of delayed instability which could be t ransmissible over many generations ; ②the frequency of recombinations increased after irradiation of the cells ; ③other abnormal karyotypes could also be observed in RSY 112 clones and HFD clones of cell , such as band loss、split and new band appearance. Which indicated delayed genetic instability.

Key words: γ-irradiation, chromosomal DNA, f requency of recombination, karyotypic alteration, bands