Cloning

The invention: Experimental technique for creating exact duplicates
of living organisms by recreating their DNA.
The people behind the invention:
Ian Wilmut, an embryologist with the Roslin Institute
Keith H. S. Campbell, an experiment supervisor with the Roslin
Institute
J. McWhir, a researcher with the Roslin Institute
W. A. Ritchie, a researcher with the Roslin Institute
Making Copies
On February 22, 1997, officials of the Roslin Institute, a biological
research institution near Edinburgh, Scotland, held a press conference
to announce startling news: They had succeeded in creating
a clone—a biologically identical copy—from cells taken from
an adult sheep. Although cloning had been performed previously
with simpler organisms, the Roslin Institute experiment marked
the first time that a large, complex mammal had been successfully
cloned.
Cloning, or the production of genetically identical individuals,
has long been a staple of science fiction and other popular literature.
Clones do exist naturally, as in the example of identical twins. Scientists
have long understood the process by which identical twins
are created, and agricultural researchers have often dreamed of a
method by which cheap identical copies of superior livestock could
be created.
The discovery of the double helix structure of deoxyribonucleic
acid (DNA), or the genetic code, by JamesWatson and Francis Crick
in the 1950’s led to extensive research into cloning and genetic engineering.
Using the discoveries ofWatson and Crick, scientists were
soon able to develop techniques to clone laboratory mice; however,
the cloning of complex, valuable animals such as livestock proved
to be hard going.
Early versions of livestock cloning were technical attempts at duplicating the natural process of fertilized egg splitting that leads to the
birth of identical twins. Artificially inseminated eggs were removed,
split, and then reinserted into surrogate mothers. This method proved
to be overly costly for commercial purposes, a situation aggravated by
a low success rate.
Nuclear Transfer
Researchers at the Roslin Institute found these earlier attempts to
be fundamentally flawed. Even if the success rate could be improved,
the number of clones created (of sheep, in this case) would
still be limited. The Scots, led by embryologist Ian Wilmut and experiment
supervisor Keith Campbell, decided to take an entirely
different approach. The result was the first live birth of a mammal
produced through a process known as “nuclear transfer.”
Nuclear transfer involves the replacement of the nucleus of an
immature egg with a nucleus taken from another cell. Previous attempts
at nuclear transfer had cells from a single embryo divided
up and implanted into an egg. Because a sheep embryo has only
about forty usable cells, this method also proved limiting.
The Roslin team therefore decided to grow their own cells in a
laboratory culture. They took more mature embryonic cells than
those previously used, and they experimented with the use of a nutrient
mixture. One of their breakthroughs occurred when they discovered
that these “cell lines” grew much more quickly when certain
nutrients were absent.Using this technique, the Scots were able to produce a theoretically
unlimited number of genetically identical cell lines. The next
step was to transfer the cell lines of the sheep into the nucleus of unfertilized
sheep eggs.
First, 277 nuclei with a full set of chromosomes were transferred
to the unfertilized eggs. An electric shock was then used to cause the
eggs to begin development, the shock performing the duty of fertilization.
Of these eggs, twenty-nine developed enough to be inserted
into surrogate mothers.
All the embryos died before birth except one: a ewe the scientists
named “Dolly.” Her birth on July 5, 1996, was witnessed by only a
veterinarian and a few researchers. Not until the clone had survived
the critical earliest stages of life was the success of the experiment
disclosed; Dolly was more than seven months old by the time her
birth was announced to a startled world.Impact
The news that the cloning of sophisticated organisms had left the
realm of science fiction and become a matter of accomplished scientific
fact set off an immediate uproar. Ethicists and media commentators
quickly began to debate the moral consequences of the use—
and potential misuse—of the technology. Politicians in numerous
countries responded to the news by calling for legal restrictions on
cloning research. Scientists, meanwhile, speculated about the possible
benefits and practical limitations of the process.
The issue that stirred the imagination of the broader public and
sparked the most spirited debate was the possibility that similar experiments
might soon be performed using human embryos. Although
most commentators seemed to agree that such efforts would
be profoundly immoral, many experts observed that they would be
virtually impossible to prevent. “Could someone do this tomorrow
morning on a human embryo?” Arthur L. Caplan, the director of the
University of Pennsylvania’s bioethics center, asked reporters. “Yes.
It would not even take too much science. The embryos are out
there.”
Such observations conjured visions of a future that seemed marvelous
to some, nightmarish to others. Optimists suggested that the best and brightest of humanity could be forever perpetuated, creating
an endless supply of Albert Einsteins and Wolfgang Amadeus
Mozarts. Pessimists warned of a world overrun by clones of selfserving
narcissists and petty despots, or of the creation of a secondary
class of humans to serve as organ donors for their progenitors.
The Roslin Institute’s researchers steadfastly proclaimed their
own opposition to human experimentation. Moreover, most scientists
were quick to point out that such scenarios were far from realization,
noting the extremely high failure rate involved in the creation
of even a single sheep. In addition, most experts emphasized
more practical possible uses of the technology: improving agricultural
stock by cloning productive and disease-resistant animals, for
example, or regenerating endangered or even extinct species. Even
such apparently benign schemes had their detractors, however, as
other observers remarked on the potential dangers of thus narrowing
a species’ genetic pool.
Even prior to the Roslin Institute’s announcement, most European
nations had adopted a bioethics code that flatly prohibited genetic
experiments on human subjects. Ten days after the announcement,
U.S. president Bill Clinton issued an executive order that
banned the use of federal money for human cloning research, and
he called on researchers in the private sector to refrain from such experiments
voluntarily. Nevertheless, few observers doubted that
Dolly’s birth marked only the beginning of an intriguing—and possibly
frightening—new chapter in the history of science.