Phenotypes of FAC knockout mice. Panels (A) (wild-type control) and (B) (FAC knockout mouse) show the results of chromosome breakage analysis. Cells were exposed to 20 ng/mL MMC for 48 hours. Multiple radial formation (arrows), gaps, and breaks can be seen in the mutant, but not control cells. Testicular histology of age-matched wild-type control (C) and FAC knockout mouse (D) at the same magnification. The normal control shows the cross-section of a seminiferous tubule containing all stages of spermatogenesis. In the mutant animal, two small abnormal seminiferous tubules can be seen. Spermatogenesis is absent and only Sertoli cells remain. Hypertrophy of interstitial tissue is also evident.