1.   Instead of using early-stage embryo cells, Wilmut used cells from the udder of an adult sheep.

2.   Instead, technicians would bathe it in proteins that direct primitive cells, embryo cells, to become marrow cells.

3.   Already, scientists in Oregon say they have cloned rhesus monkeys from very early embryo cells.

4.   And if you can grow a human from a single embryo cell, is that cell the moral equivalent of an entire embryo?

5.   After the animal was born, the scientists could ascertain whether any of the added genes were taken up by the embryo cells.

6.   But could Wilmut and Campbell have mixed up the cells, using embryo cells from a Finn Dorset by accident?

7.   But now, as scientists are eyeing human embryo cells as material for research, the experiment is giving rise to a thorny philosophical question.

8.   But this time, since it was an embryo cell that was involved, the development was more likely to proceed.

9.   Few embryo cells take up the added genes, and even fewer use them.

10.   First, it is impossible to grow embryo cells in culture without having them change into something that looks like skin cells.