Table III. Chromosomal aberrations induced by irradiation during G₂ and late S–G₂ phase.

Genotype	1.5 h				3 h
	Chromatid	Isochromatid	Exchanges	Total	Chromatid	Isochromatid	Exchanges	Total
wild type	28	6	0	34 ± 6	11	4	0	15 ± 4
ATM–/–	40	9	1	50 ± 6	19	11	0	30 ± 5
KU70–/–	58	7	4	69 ± 8	10	7	1	18 ± 4
RAD54–/–	37	10	1	48 ± 7	19	5	1	25 ± 5
ATM–/–/KU70–/– #1	131	13	0	144 ± 12	113	17	1	131 ± 11
ATM–/–/KU70–/– #3	nd	nd	nd	nd	77	71	0	148 ± 9
ATM–/–/RAD54–/– Rad54+	28	9	0	37 ± 6	32	4	0	36 ± 8
ATM–/–/RAD54–/– Rad54–	43	8	0	51 ± 7	26	8	0	34 ± 8

Cells were subjected to 0.3 Gy γ–irradiation, then incubated with colcemid for 1.5 or 3 h, as indicated, and harvested. At least 100 metaphases at 1.5 h and at least 50 at 3 h were analysed. The data from ATM^–/–RAD54^–/–Rad54^– cells were obtained after 5 days of Rad54 repression. Data were calculated and are presented as described for Table I. nd, not determined.