Even the early sea-urchin embryo can be separated into single cells and will reform a more or less normal embryo.

Driesch provided further examples of regulation, for, even at the four-cell stage each cell could develop into a perfectly normal embryo.

That is because in normal embryo development, certain genes from the father but not the mother, or vice versa, are turned on.

When those cells were activated to divide, they produced apparently normal early embryos.

BMP4 is a product that contributes to the development of the skeleton in the normal embryo.

At the moment, we cannot identify with any certainty the eggs that will develop into normal embryos.

But with this method normal male embryos are discarded along with the ones carrying the defect.

But cloned embryos may not be genetically equivalent to normal embryos.

Is there such a thing as a 'normal' embryo?

The tissues are disorganized and do not develop into a normal embryo.