Single crypts having deficient expression for Pms2 (A), Ercc1 (B) or Xpf (C). These crypts are from a histologically normal area of a colon resection of a male patient who had an adenocarcinoma in the sigmoid colon. When Pms2 is deficient, typically all the cells of the crypt have low or absent expression for Pms2 (A). When Ercc1 is deficient, cells of the "body" have reduced or absent expression of Ercc1 but cells of the "neck" and "surface" usually have high expression for Ercc1 (B). When Xpf is deficient, cells of the body have reduced or absent expression of Xpf, but cells of the neck region often have high expression of XPF. Cells at the surface may have reduced expression (C) or may have high expression for Xpf (not shown here but see Figure 4). Images taken at 200×.