Atm deficiency results in chromosomal instability

GenotypeBreaks per metaphase (± SE)n
+/+0.71  ±  0.2228
+/−0.88  ±  0.2817
−/−4.56  ±  0.48 (× 6.4)52
+/+, Bleomycin1.70  ±  0.3920
−/−, Bleomycin9.71  ±  0.99 (× 5.7)41
  • Metaphase chromosomes were prepared from embryonic fibroblasts of wild-type (+/+), heterozygous (+/−), or homozygous (−/−) Atm mutant mice, either with or without bleomycin treatment. Data are presented as the average of the number of double-stranded breaks observed per metaphase. The fold-increase in Atm homozygotes vs. wild-type controls is also noted.