To make copies. Bone marrow Bone marrow: The soft, spongy tissue inside most bones. Blood cells are formed in the bone marrow. stem cells stem cells: Cells in the body that develop into other cells. There are two main sources of stem cells. Embryonic stem cells come from human embryos and are used in medical research. Adult stem cells in the body repair and maintain the organ or tissue in which they are found. Blood-forming (hemapoietic) stem… clone themselves all the time. The cloned stem cells eventually become mature blood cells that leave the bone marrow and enter the bloodstream.
