Nuclear transfer is the process of creating an embryo by fusing an adult animal cell, in Dolly's case, an udder cell from a sheep, into an enucleated egg cell.

1. A donor cell has to be forced into the Gap Zero, or G0 cell stage, a dormant phase, in which it shuts down its active genes and current definitions (e.g. to be a skin cell) and thus has the ability to take on another definition.
2. The donor animal cell is put it into an unfertilised egg cell (an oocyte) whose nucleus has been removed, so that what remains provides the cellular machinery required in the formation of an embryo.
3. An electric pulse fuses the two cells. Genes in the donor animal cell enter the egg.
4. Another electric pulse awakens the genes. The fused cells divide and form an embryo.
5. The embryo is implanted inside a surrogate mother to divide and grow normally. The resulting organism is a clone as it has the same genetic material as the donor body cell.

Scientists are still unsure of why an electric pulse sent to the two cells causes them to meld together and activates development in the egg, even though they have been carrying out this step for years in the process of cloning. However, they have learnt that the shock doesn't fully mimic the activation process of a sperm, which could explain why very few embryos survive beyond the first few days of formation.

The Process of Nuclear Transfer (Microinjection)

Microinjection can be said to be a subset of nuclear transfer (fusion). While nuclear transfer (fusion) is fusing an entire adult animal cell into an egg cell whose nucleus has been removed, the microinjection technique uses only the adult cell nucleus.

1. The donor nucleus (in the G0 state : see The Process of Nuclear Transfer) is put it into an unfertilised egg cell whose nucleus had been removed.
2. An electric pulse fuses the nucleus with the cell.
3. The cell is implanted inside a surrogate mother to grow as a normal embryo. The resulting organism is a clone as it has the same genetic material as the nucleus.

Artificial Twinning

Artificial twinning, is the process of splitting an embryo into two or more embryos.

1. An egg cell is fertilised by sperm, then left to grow into an embryo.
2. The embryo is split into two or more embryos when it is still in the early cell stage.
3. The split embryos are nurtured into new embryos, all genetically identical, then implanted into surrogate mothers to grow.
4. This process is not the same as nuclear transfer as the born animal has biological parents, and is a clone of its brothers and sisters. In nuclear transfer, the born animal is a clone of its parent.

* An interesting point to note is that no one really knows why an embryo splits in the process of natural twinning, from which natural identical twins are formed.