7 Ian Wilmut 7embryonic cell nuclear transfer by using cultured embryonic
cells that were nine days old. This was similar to the exper-
iment that led to the creation of Megan and Morag.
How ever, the new experiment involved a different sheep
breed; the cells used for nuclear transfer came from a Poll
Dorset sheep. This first experiment resulted in the birth
in 1996 of four Poll Dorset clones: Cedric, Cecil, Cyril, and
Tuppence. In the second experiment, the team used fetal
fibroblasts isolated from sheep fetuses after 26 days of devel-
opment; these cells served as nucleus donors for transfer
into an enucleated egg. This experiment resulted in the birth
of two clones, Taffy and Tweed. In the third experiment, the
scientists isolated adult cells (in this case, mammary gland
cells) from a six-year-old ewe and used these cells as nucleus
donors for transfer into egg cells; this technique inspired
the later development of a procedure called somatic cell
nuclear transfer (SCNT). Wilmut and his team constructed
277 embryos containing adult cell nuclei that were implanted
into 13 surrogate mothers, only one of which became preg-
nant. This pregnancy was carried to term successfully. The
Finn Dorset lamb, born on July 5, 1996, was Dolly.
In 1997, following the publication in the journal Nature
of a summary of their research leading to Dolly, Wilmut,
Campbell, and the Roslin Institute instantly became
known for having opened the door to a new era of contro-
versial cloning research. The cloning of Dolly generated
speculation in the media and in the scientific community
about the possibility of cloning humans. Wilmut considered
human cloning impractical for both ethical and scientific
reasons. From his work with sheep, he knew the dangers
of cloning; many embryos died following implantation,
and those embryos that survived and developed to term as
full-grown fetuses sometimes died immediately following
birth or were born with birth defects.