4. Human cloning

You might not believe it, but there are human clones among us right now. They weren't made in a lab, though: they're identical twins, created naturally. Below, we'll see how natural identical twins relate to modern cloning technologies.

Despite several highly publicized claims, human cloning still appears to be fiction. There currently is no solid scientific evidence that anyone has cloned human embryos.

In 1998, scientists in South Korea claimed to have successfully cloned a human embryo, but said the experiment was interrupted very early when the clone was just a group of four cells. In 2002, Clonaid, part of a religious group that believes humans were created by extraterrestrials, held a news conference to announce the birth of what it claimed to be the first cloned human, a girl named Eve. However, despite repeated requests by the research community and the news media, Clonaid never provided any evidence to confirm the existence of this clone or the other 12 human clones it purportedly created.

In 2004, a group led by Woo-Suk Hwang of Seoul National University in South Korea published a paper in the journal Science in which it claimed to have created a cloned human embryo in a test tube. However, an independent scientific committee later found no proof to support the claim and, in January 2006, Science announced that Hwang's paper had been retracted.

From a technical perspective, cloning humans and other primates is more difficult than in other mammals. One reason is that two proteins essential to cell division, known as spindle proteins, are located very close to the chromosomes in primate eggs. Consequently, removal of the egg's nucleus to make room for the donor nucleus also removes the spindle proteins, interfering with cell division. In other mammals, such as cats, rabbits and mice, the two spindle proteins are spread throughout the egg. So, removal of the egg's nucleus does not result in loss of spindle proteins. In addition, some dyes and the ultraviolet light used to remove the egg's nucleus can damage the primate cell and prevent it from growing.

Part 2. Practical application of cloning

2.1. Reasons for cloning

Research advances over the past decade have told us that, with a little work, we humans can clone just about anything we want, from frogs to monkeys and probably even ourselves!

So, we can clone things, but why would we want to? Let's look at some of the reasons people give to justify cloning.

1. Cloning for medical purposes

Of all the reasons, cloning for medical purposes has the most potential to benefit large numbers of people. How might cloning be used in medicine?

Much of what researchers learn about human disease comes from studying animal models such as mice. Often, animal models are genetically engineered to carry disease-causing mutations in their genes. Creating these transgenic animals is a time-intensive process that requires trial-and-error and several generations of breeding. Cloning technologies might reduce the time needed to make a transgenic animal model, and the result would be a population of genetically identical animals for study.

Cloning stem cells for research

Stem cells are the body's building blocks, responsible for developing, maintaining and repairing the body throughout life. As a result, they might be used to repair damaged or diseased organs and tissues. Researchers are currently looking toward cloning as a way to create genetically defined human stem cells for research and medical purposes. To see how this is done, see Creating Stem Cells for Research, a component of the Stem Cells in the Spotlight module.

"Pharming" for drug production

Farm animals such as cows, sheep and goats are currently being genetically engineered to produce drugs or proteins that are useful in medicine. Just like creating animal models of disease, cloning might be a faster way to produce large herds of genetically engineered animals. Find out more about this research in the feature article Pharming for Farmaceuticals.

2. Reviving Endangered or Extinct Species

Have you seen Jurassic Park? In this feature film, scientists use DNA preserved for tens of millions of years to clone dinosaurs. They find trouble, however, when they realize that the cloned creatures are smarter and fiercer than expected.

Could we really clone dinosaurs?

In theory? Yes. What would you need to do this?

A well-preserved source of DNA from the extinct dinosaur, and

A closely related species, currently living, that could serve as a surrogate mother

In reality? Probably not. It's not likely that dinosaur DNA could survive undamaged for such a long time. However, scientists have tried to clone species that became extinct more recently, using DNA from well-preserved tissue samples. For an example, see "Can we really clone endangered or extinct animals?" on the right side of this page.

3. Reproducing a Deceased Pet

No joke! If you really wanted to, and if you had enough money, you could clone your beloved family cat. At least one biotechnology company in the United States offers cat cloning services for the privileged and bereaved, and they are now working to clone dogs. But don't assume that your cloned kitty will be exactly the same as the one you know and love. Why not? See Cloning Myths.

4. Cloning Humans?

To clone or not to clone: that is the question. The prospect of cloning humans is highly controversial and raises a number of ethical, legal and social challenges that need to be considered. To explore some of these, see What are Some Issues in Cloning?

Why would anyone want to clone humans? Some reasons include:

To help infertile couples have children

To replace a deceased child. [9]

In the United States, the human consumption of meat and other products from cloned animals was approved by the FDA on December 28, 2006, with no special labeling required because food from cloned organisms has been found to be identical to the organisms from which they were cloned.[5]