Table 1.

Spontaneous chromosome aberrations in nontransformed cells

Cell type	No. cells scored	Gaps, breaks, and deletions*	Total exchange-type aberrations†	Telomeric fusions‡	Telomeric fusions per cell
WT (p3,4)§	100	26	3	0	0.000
scid (p5,6)	91	47	22	15	0.165
p53−/− (p3,5)	100	57	10	1	0.010
p53−/−/scid (p5,6)	100	12	10	8	0.080

*Nonexchange-type aberrations are combined into a single category. 

^† All identifiable exchange-type aberrations, i.e., chromosome and chromatid dicentrics, metacentrics, and rings are included in this category. Many Ku^−/− cells had small, difficult to classify, yet clearly aberrant, chromosomes. Their frequency, and the fact that some appear to be clonal in origin, indicates they are not lethal to the cells possessing them. They are not included in aberration counts. 

^‡ Number of exchange-type aberrations having telomere sequence at points of fusion. 

^§Passage numbers.