The premature chromosome condensation technique was used to estimate the dosage effect on the G2-chromosome breaks in HO8910 after exposure toγ-rays

and to investigate the time effect on the rejoining of the G2-chromosome breaks. The results show that the number of G2 chromatid-type breaks linearly increased with doses and the number of G2 iso-chromatid breaks increased with dose in a linear-square manner. With the prolongation of culture time

G2 chromatid-type breaks obviously got repaired

and almost 65% chromatid-type breaks got repaired in the early 24 hour post-irradiation

whereas only about 20% iso-chromatid breaks got repaired during the same time. Furthermore

the rejoining of the two types of chromatid breaks occurred mostly in 2 hours after irradiation and from 12 to 24 hours after irradiation

the number of chromatid breaks was found to get stabilized basically

which indicates that the repairing process is over in the early 24 hours of post-irradiation.