Final answer:
Graft-versus-host disease is the primary source of rejection in bone marrow transplants. Genetic differences, particularly in the MHC genes, influence the likelihood of rejection in transplant recipients.
Step-by-step explanation:
Graft-versus-host disease (GVHD) is the primary source of rejection in bone marrow transplants. GVHD occurs when the mature T cells in the transplanted tissue recognize the recipient's tissues as foreign. The donor's T cells, once activated, attack the recipient cells, causing acute GVHD. Genetic differences, especially among the MHC (HLA) genes, dictate the likelihood of rejection in transplant recipients.