Tartrate-resistant acid phosphatase staining of representative bone marrow sections from 12-month-old heterozygous F1 Gata1^low females carrying the mutation in a predominantly C57BL/6 and in hemizygous F2 males of CD1 and DBA/2 backgrounds, as indicated. Staining of the corresponding sections from wild-type littermates also are indicated. Results are representative of those obtained in 3 animals per experimental group. The presence of osteoblasts is indicated by arrows. Original magnification, × 20.