Cytogenetic studies demonstrating donor origin of leukemic cells. Composites of the 22 chromosomes from pretransplantation (study no. 1), 6 months after transplantation, when molecular studies demonstrated 100% donor chimerism (study no. 2), and following diagnosis of AML (study no. 3), illustrating informative G-band polymorphism. One donor chromosome 22 has an enlarged short arm and satellite region, designated by the arrow. This polymorphism is seen in studies 2 and 3, suggesting donor origin of the leukemic cells. G-band polymorphisms represent regions that differ between individuals but have no clinical significance. They are most commonly seen on acrocentric chromosomes such as chromosome 22.