Surprisingly, cells that will form the gut are on the outside surface of many early embryos.

But does regulation continue throughout development, or is it just a property of the early embryo?

It is possible to label the cells of the early embryo and follow what they do during development.

The early embryo is "a flat little sheet that gets folded," she said.

The most potent and versatile type of stem cell comes from very early embryos.

But this approach won't satisfy those who believe that even a single cell removed from an early embryo may have the potential to produce life.

And an early embryo looks like nothing so much as a plate of cells.

But the problem was that cells from early embryos were not good for genetic engineering.

They were cloning cells from early embryos that had not yet specialized.

Until the 16-cell stage, the early embryo is symmetrical and all cells are equal.