The Facts and Fiction of Cloning

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 injury.

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 reality.

"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 cloning.

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.