Bif-1 haploinsufficiency promotes Myc-induced genomic instability in prelymphomatous splenocytes. Spleens were isolated from 9-week-old prelymphomatous Eμ-Myc–transgenic and age-matched control mice with the indicated Bif-1 alleles. (A) Tissue lysates were subjected to immunoblot analyses using the indicated antibodies. (B-C) The karyotypes of Bif-1^+/+ (n = 151 from 3 mice), Bif-1^+/− (n = 153 from 3 mice), Bif-1^−/− (n = 154 from 3 mice), Eμ-Myc/Bif-1^+/+ (n = 268 from 5 mice), Eμ-Myc/Bif-1^+/− (n = 384 from 7 mice), and Eμ-Myc/Bif-1^−/− (n = 127 from 2 mice) splenocytes were analyzed. At least 50 metaphases were evaluated for each mouse. Representative images and magnified images of chromosomes are shown in panel B and the insets in panel B, respectively. The percentage of aneuploidy and the number of chromosomes per cell are shown in panels C (mean ± SD) and D, respectively. Statistical significance was determined using a Wilcoxon rank-sum test with continuity correction. *P < .01.