TABLE 1.

Spontaneous SCE in mouse ES cells^a

No. of SCE events per chromosome	Percentage of events in:
	Wild type	Recql5−/−	Blm−/−	Recql5−/−Blm−/−
0	82.0	59.6	54.6	42.4
1	16.4	25.5	32.1	29.3
2	1.52	10.7	11.0	19.2
3	0.13	3.19	2.10	6.47
4	0	0.69	0.09	1.31
≥5	0	0.27	0.09	1.26

^aTotal chromosomes were derived from 56, 80, 30, and 48 metaphase spreads of the wild type, Recql5^−/−, Blm^−/−, and Blm^−/− Recql5^−/− ES cells, respectively. Total chromosomes were 2,238 for the wild type, 2,913 for Recql5^−/−, 1,142 for Blm^−/−, and 1,902 for Blm^−/−Recql5^−/− ES cells. The total number of SCE events was 251 for the wild type, 1,769 for Recql5^−/−, 829 for Blm^−/−, and 1,884 for Blm^−/−Recql5^−/− ES cells. The average number of SCEs per chromosome (values in parentheses are standard errors) was 0.198 (0.009) for the wild type, 0.607 (0.016) for Recql5^−/−, 0.614 (0.023) for Blm^−/−, and 0.991 (0.025) for Blm^−/−Recql5^−/−.