Transplantation of Polg^A marrow into Polg⁺ recipients recapitulates age-related macrocytic anemia and leukopenia of Polg^A mice. Two-month-old B6.SJL hosts were lethally irradiated and then reconstituted with 5 × 10⁶ nucleated marrow cells from 2-month-old donor mice. Peripheral-blood samples were analyzed as in Figure 1 from 2 to 8 months after transplantation (4-10 months of age). Each point represents the mean ± SEM of recipients of Polg⁺ marrow (n = 9, solid lines) and recipients of Polg^A marrow (n = 5, dotted lines). (A) Hemoglobin levels. (B) Mean corpuscular volume of all RBCs (□) and of reticulocytes only (◇). (C) Platelet count. (D) White blood cell (WBC) count. (E) Representative Wright-Giemsa–stained images of RBCs and lymphocytes from peripheral blood smears of 15-month-old mice. Bars represent 10 microns. * P < .05 (statistical significance) by Student t test; **P < .01