As organisms develop, their cells differentiate , transforming early embryonic cells into specific types of cells - liver, muscle, udder, etc. Scientists thought that once differentiation occurred, liver cells could only make more liver cells, muscle cells could only make more muscle cells, and udder cells could only make more udder cells. Dolly's birth showed that this process is actually reversible, and udder cells can make a complete sheep. Cloning is not a one-time fluke. Medicine One of cloning's most promising applications involves stem cells.
Stem cells have the ability to generate a variety of cell types.
This makes them very useful for the treatment of a number of diseases. For example, replacement of cancerous stem cells in bone marrow with healthy stem cells from a donor is used to treat leukemia. In many cases, though, the patient's immune system rejects the donated cells. Cloning solves this problem. If the person's own cells can be used to generate stem cells, there would be no risk of rejection.