Human Reproductive Cloning - Brutes or Angels: Human Possibility in the Age of Biotechnology - page 181

tially skeptical about actually performing such a feat. The cause for this
skepticism was that for a specialized somatic cell to perform its specialized
functions, most of its genes must be kept inactive. for example, the genes
for muscle fiber proteins are active inside muscle cells, but genes for other
proteins, such as hair, insulin, hemoglobin, growth hormone, and gut di-
gestive enzymes, are turned off in muscle cells. restoring complete ge-
netic potential ( totipotency ) to somatic cell DnA and reactivating thousands
of genes in just the right sequence to orchestrate the development of a new
organism seemed beyond the reach of laboratory science. But science and
living cells do amazing things, and the doubters were wrong.
in 1966 two developmental biologists, John Gurdon at oxford Univer-
sity and v. Uehlinger at the University of Geneva, reawakened the devel-
opmental potential in the DnA of a single cell from a tadpole to produce an
entirely new tadpole. They did this by transferring the DnA-containing
nucleus from a cell in the tadpole's gut into an egg cell denuded of its own
nucleus. When the gut cell nucleus found itself surrounded by the envi-
ronment of the egg cytoplasm, its DnA began to behave like the DnA in
a newly fertilized egg. The DnA replicated and the host egg cell divided
into two cells. more cycles of cell division followed, producing a frog em-
bryo that eventually grew into a normal tadpole, a genetic clone of the tad-
pole that donated the somatic cell DnA.
The work of Gurdon and Uehlinger (1966) demonstrated that totipo-
tency is inducible in highly specialized cell types. it also opened new ave-
nues of research to learn how cells become functionally specialized during
normal development, knowledge with relevance for preventing and treat-
ing cancer and preventing birth defects. reports of cloned mice and even
a cloned person in the 1970s turned out to be bogus. But on february 23,
1997, scottish reproductive biologist ian Wilmut jolted biology and hu-
manity to the reality of mammalian cloning (Wilmut et al. 1997). on that
day he introduced the world to Dolly, a seven-month-old lamb created
from the genetic information in a single cell from an adult ewe (fig. 7.1).
As with the cloned frog, Dolly was created by introducing the nucleus
from a somatic cell into an enucleated egg, one from which the nucleus has