1.   Although scientists could transfer nuclei from adult cells to egg cells, the frogs only developed to tadpoles, and they always died.

2.   And no one expected an egg cell to be able to reprogram such an adult cell, somehow stripping its genes bare of their chemical masks.

3.   And that led him to the research that resulted in the birth of the sheep named Dolly, the first animal cloned from an adult cell.

4.   Before the adult cell is used to start cloning, scientists could alter it.

5.   A dispute will continue, however, over the use of embryonic rather than adult cells.

6.   ACT officials said last November that they had combined adult human cells with cow eggs that had been stripped of their nucleus.

7.   Adult cells typically have their genes permanently switched off, save those needed for specific roles.

8.   Adult cells also have a more limited ability to specialize.

9.   After all, an adult cell, like an udder cell, has reached its final destiny in the body and under normal circumstances never changes into something else.

10.   But adult cells appear limited by their environment.