In practice a few frogs have been produced by killing the egg nucleus by ultraviolet irradiation, and replacing it with the nucleus from a cell of the gut of a tadpole.

Quite the contrary, all the evidence from experiments with mice, which have been intensively studied, shows that it is not even possible for the nucleus of a very early embryonic mouse cell to substitute for the egg nucleus.

If such cells develop as they do because they contain only some of the genes - for example, just the genes for being a gut cell - then a nucleus from such a cell could not substitute for an egg nucleus.

It is not clear whether fertilization of the egg nucleus takes place while the fruit is still on the tree or months after it has fallen.

They also want to develop embryonic stem cells by nuclear transfer, the replacement of an egg nucleus with one from an adult cell.

The cell in which the egg nucleus develops and is fertilized (the carpogonium) elongates, divides and a curved row of 5 or 6 cells is formed.

So far, Dr. Grifo has shown that he can move egg nuclei around, which is, in essence what is required for cloning.