The Facts and Fiction of Cloning
Understanding the real science behind the headlines and the hubbub.
Cloning. More than ever, the
word stirs emotion and triggers debate, as what was once science fiction
becomes scientific fact. Just what are researchers working on and why? Do we
have anything to gain, or to lose, from their continued efforts?
For the first time, researchers have successfully cloned a
human embryo -- and have extracted stem
cells, the body's building blocks, from the embryo. Stem cells are
considered one of the greatest hopes for curing diseases like diabetes, Parkinson's disease, and paralysis caused by spinal cord
What Is Cloning?
Before you decide where you stand on this debate, you'll need
to understand where the science is today. To put it all in perspective, WebMD
asked some renowned scientists to explain precisely what cloning is and what it
isn't. Popular depictions -- from the ominous hordes of worker drones in the
futuristic novel Brave New World to Michael Keaton's comic time-saving
duplicates in the film Multiplicity -- have almost nothing to do with
"Clones are genetically identical individuals," says
Harry Griffin, PhD. "Twins are clones." Griffin is assistant director
of the Roslin Institute -- the lab in Edinburgh, Scotland, where Dolly the
cloned sheep was created in 1997.
Usually, after sperm and egg meet, the fertilized cell begins
dividing. Remaining in a clump, the one becomes two, then four, eight, 16, and
so on. These cells become increasingly specialized to a particular function and
organize into organs and systems. Eventually, it's a baby.
Sometimes, though, after the first division, the two cells
split apart. They continue dividing separately, growing to become two
individuals with the exact same genetic make-up -- identical twins, or clones.
This phenomenon, though not entirely understood, is far from unusual. We've all
known identical twins.
Early on, says Griffin, the term cloning referred to embryo
splitting -- doing in the lab what happens in the woman's body to create
identical twins. "It was first done in cattle, but there are one or two
human examples." Those human embryos were never implanted, he says.
"Twins were not deliberately created, but they certainly could be."
When we speak of cloning nowadays, however, we're referring not
to embryo splitting, but to a process called nuclear transfer. "The
importance is that with nuclear transfer, you can copy an existing
individual, and that's why there's controversy," says Griffin.
In nuclear transfer, DNA from an unfertilized egg is removed
and replaced with DNA from an adult body cell -- a skin cell, for example. When
the process works, the manipulated cell -- coaxed by the newly-implanted
genetic material -- begins to divide and eventually becomes a genetic replica
of the adult-cell donor. The process produces a new individual whose identical
twin is not a minute or two older, but already grown up.
Now, researchers in South Korea and the University of Michigan have cloned a
human embryo. This is not cloning to make a genetically matched baby, but
cloning for research purposes -- also called therapeutic cloning or research
This new development means that therapeutic cloning -- the ability to create
human clones for research purposes -- is no longer a theory, but a reality. And
it's sure to reignite the controversy of whether to ban all cloning or to allow
some cloning for therapeutic purposes.
Therapeutic cloning is not new. Scientists have used the technology to cure
a variety of diseases in mice. Scientists have also studied the potential uses
of human stem cells culled from embryos leftover in fertility clinics.