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Unformatted text preview: mary epithelial cell that
was transplanted into an unfertilized egg in place of the normal egg
nucleus—a process called somatic cell nuclear transfer. It is interesting to
note that this type of experiment was first carried out in frogs in the 1950s.
The fact that it took over 40 years before it was successfully performed in
mammals attests to the technical difficulty of the procedure. Since the initial
success of Wilmut and his colleagues, transfer of nuclei from adult somatic
cells into enucleated eggs has been used to create cloned offspring of a variety of mammalian species, including sheep, mice, pigs, cattle, goats, rabbits,
and cats. However, cloning by somatic cell nuclear transfer in mammals
remains an extremely inefficient procedure, such that only 1–3% of embryos
generally give rise to live offspring.
Animal cloning by somatic cell nuclear transfer, together with the properties of embryonic stem cells, opens the possibility of therapeutic cloning
(Figure 17.26). In therapeutic cloning, a nucleus from an adult human cell
would be transferred to an enucleated egg, which would then be used to
produce an early embryo in cultu...
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