But I wish cows laid eggs and Daddy had figured out how to bring cow eggs along.

The human nuclei are thought to take over the cow egg, so that the hybrid embryo quickly becomes human during the few days it lives.

The cells are obtained by fusing a human skin or blood cell with a cow egg whose own nucleus has been removed.

The cow egg is thought to make the nucleus of the human cell revert to the embryonic state.

They use cow eggs because these are far cheaper and more available than human eggs and raise no ethical problems.

The company favors cow eggs over human eggs because the former are cheap, available and uncontroversial.

Factors in the cow egg are thought to make the human cell nucleus revert to its embryonic form.

They took one of those embryo cells and merged it with a second cow egg whose own nucleus has been removed.

Researchers get thousands of cow eggs from slaughterhouses, Dr. Page said.

So they added cells that were dividing normally to unfertilized cow eggs whose own genetic material had been removed.