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Cloning

Author(s): Joseph G. Marx, PhD

Somatic Cell Nuclear Transfer (SCNT): Dolly – The First True Clone (1997)

The first successful outcome using SCNT to produce a viable organism was a sheep named Dolly. Scientists removed the nucleus from a mammary (breast) cell of a six-year old sheep and injected it into an empty sheep egg cell. Electric current was used to "shock" the nucleus to begin mitotic division (nuclear division). After a certain number of cell divisions, the ball of cells was implanted into a pseudo-pregnant sheep. (Pseudo-pregnant sheep are female sheep given hormone injections to prepare the uterine lining so the SCNT-created embryo will be accepted readily.) Dolly was born as the first reproductively cloned animal.

As described on the slide, the researchers were able to combine 434 eggs with nuclei. Only 29 of those 434 eggs actually started to divide. All 29 were implanted into pseudo-pregnant sheep. Out of these 29, only one sheep, Dolly, was born. Thus, the first successful attempt had a success rate of 0.2%. This demonstrated for the first time that the DNA in a somatic cell (specifically, a breast cell) still contained all the information needed to direct the formation of an entire organism, and that this information could be made accessible again in the adult cell.