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Cloning: Frequently Asked Questions
A Look at the Science and Controversy

What are the different forms of cloning?
How is a clone created?
What animals have been cloned?
Why is cloning so difficult?
What's the relationship between cloning and stem cells?
Why create a clone?
Why the controversy?
Is human cloning banned in the U.S.?
What countries have banned human cloning?

What are the different forms of cloning?

This is where the confusion starts. The phrase cloning means different things to different people. A clone is a genetic copy of another organism. What cloning has come to mean to most people is to produce a baby animal that will become an exact duplicate of a single adult animal. That process is called "reproductive cloning."

But to scientists and ethicists, cloning also has another meaning: the creation of an embryo -- from the genetic material of a single organism -- that will never be allowed to develop beyond a clump of cells, and will never be implanted into a woman. This is considered "non-reproductive" or "therapeutic" cloning.

Nearly every poll shows virtually unanimous support for a ban on reproductive cloning. On the other hand, opposition to cloning that would produce an embryo but not a baby is not as vehement. Scientists are in favor of allowing this, and even President Bush’s conservative Council on Bioethics was narrowly in favor of supporting it. Scientists want to make and study cloned embryos because they see great promise for understanding and ultimately treating disease. "Therapeutic cloning" is also sometimes called "research cloning." But scientists try to steer clear of the label "research cloning" because it tends to evoke images of mad scientists at work.

Scientists also sometimes refer to the non-reproductive form of cloning as "nuclear transplantation."

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How is a clone created?

"Nuclear transplantation" is the procedure through which clones are created. Researchers take a cell from the adult animal they want to clone. The nucleus of this cell contains the animal's genome -- i.e., the DNA that contains the instructions to make a new individual.

Next, an unfertilized egg is taken from a female of the same species, and its nucleus is removed. Researchers then insert the nucleus from the adult cell into the egg, essentially replacing the egg's DNA with that of the animal being cloned.

The donor cell's nucleus is fused with the egg cell by passing a small electric current through the cell. A series of chemicals is then added to trick the egg into "thinking" it's been fertilized. If this is successful, and the egg starts to divide, its future growth and development is determined by the unique genetic instructions in the transferred nucleus.

In other words, the egg grows into a genetic copy of the animal from which the nucleus came. This cloned embryo will grow in the lab for several days and possibly a few weeks. This is what researchers work with in therapeutic cloning. But for the embryo to develop into a baby animal, it has to be implanted into the uterus of a female of the same or closely related species, i.e. reproductive cloning.

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What animals have been cloned?

Cloning animals has not been controversial. So far sheep, goats, pigs, cows, mice, rabbits, horses and cats have been cloned. But cloning is still not easy to do, and researchers haven't been able to clone monkeys, and until recently, human embryos. Korean scientists reporting in a February 2004 edition of Science magazine were able to clone a human embryo and harvest stem cells from it. A first in human cloning, the embryo survived through the blastocyst stage, but was not implanted in a woman. (Blastocysts are a hollow ball of about a hundred cells from which stem cells can be obtained.)

For reasons that are little understood, many cloned embryos do not develop properly. They die before or shortly after birth. It's also clear that cloned animals that grow to adulthood may have unexpected defects, such as heart or respiratory problems that do not appear until later in life.

audio icon Listen to a Science Friday discussion on problems detected in cloned animals.

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Why is cloning so difficult?

No one knows the answer to this for certain, but there are some obvious possibilities. Cloning takes the whole notion of sexual reproduction and throws it out the window. Egg and sperm are unique, highly specialized cells in our bodies. Their function is to take DNA from two distinct individuals and shuffle and join it so that it becomes the unique genetic code for a third, distinct individual. The DNA bundles in egg and sperm are in a special "starter" state that enables them to combine with each other and orchestrate the complex series of steps needed to turn a clump of cells into an entire person.

No other cells in the body are designed to do this. There are more than 200 different cell types in the human body. Each has its own special function -- red blood cells perform an entirely different function than heart muscle cells, nerve cells or skin cells, for instance. Once a cell has its special function, physical changes take place in its DNA that prevent it from switching careers. A hair follicle that suddenly started producing liver cells on the top of a person's head would be disconcerting, not to mention messy.

But in cloning, the DNA of an "ordinary" adult cell -- whether it's a skin cell or a kidney cell - is essentially being forced to assume the powerful and versatile starter state normally found only in egg and sperm. That switching or transforming process, known as reprogramming, occurs when the adult cell nucleus is inserted into an egg whose own nucleus has been removed. There are special proteins in the egg cytoplasm that facilitate reprogramming. Most scientists believe cloning fails so frequently because this reprogramming doesn't work properly. Indeed, some scientists believe it never works properly, and that no cloned animal is completely normal.

Just as mysterious is why some animals are easier to clone than others. Frogs were cloned decades ago, but Dolly the sheep was the first mammal to be cloned. Since then several other mammalian species have been cloned. Despite a large team working on the project, scientists have not succeeded in cloning a dog, although the same team did clone a cat. Likewise no one has succeeded in cloning a monkey.

audio icon Listen to an NPR report on the difficulties of cloning.

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What's the relationship between cloning and stem cells?

Scientists think that some day, embryonic stem cells will become the basis for what's called regenerative medicine.

The term "embryonic stem cells" refers to a type of cell that seems only to be found in very early embryos. Embryonic stem cells are a kind of "universal cell" that have the ability to become any kind of cell in the body. They form when the embryo is about five days old and is a clump of about 250 cells -- still barely visible to the naked eye.

At this point, the embryo is a hollow ball made of two types of cell arranged in two layers. Think coconut. The outside layer is made up of cells that will go on to form the placenta and other bits and pieces that anchor and nourish the embryo as it grows in the womb.

The inside layer is the inner cell mass, and it's these cells that are the embryonic stem cells. As an embryo develops, these stem cells give rise to all the specialized cells that make up the different tissues of the body. How a stem cell knows what to turn into is a mystery.

The idea behind regenerative medicine is to take these "universal" cells and persuade them to turn into the specific cell type needed to cure a disease or repair injured tissue. In other words, to supply healthy cells that can be used to replace defective or damaged ones. Consider diabetes. In one form of the disease, cells that produce insulin are destroyed. If they could be replaced with embryonic stem cells that have been "told" to become insulin-producing cells, diabetes might in theory be cured.

But there's a catch. Just as a transplanted organ is rejected by a patient's body, so are transplanted cells. That's where cloning comes in. If researchers could use cloning to grow an embryo from one of a patient's own cells, then harvest its stem cells to treat that patient, the rejection problem is solved.

audio icon Listen to a Science Friday discussion on advances in stem cell research.

Read a stem cell primer, from the National Institutes of Health.

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Why create a clone?

There are certain fertility problems that could make cloning a couple's only option if they wanted to have a baby that is genetically related to one of them. That’s why University of Kentucky researcher Panayiotis Zavos and Italian fertility specialist Severino Antinori say they want to clone human beings.

The company Clonaid, an entity created by the religious sect the Raelians, says it wants to clone humans because they were directed to by space aliens. Raelians believe cloning is how life on Earth began.

In the case of cloning to make stem cells, scientists say that technique might be the only way to make stem cells that can actually be used therapeutically.

As for cloning animals, scientists see that as an easy way to insert genes into animals. Cloning doesn't have to be done with a fresh cell taken from an adult animal. It can be done with cells that have been taken from an animal and then grown in the laboratory. Scientists are pretty good at inserting genes into cells growing in the lab, so once they get the gene they want into a cell, then they can use that cell to make a clone.

audio icon Listen to a Science Friday interview with Zavos.

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Why the controversy?

Since human cloning seemed to fall more in the world of science fiction than science fact, ethicists largely ignored the topic prior to the late 1990s. Then, in 1997 -- faced with Dolly the cloned sheep, President Clinton asked his National Bioethics Advisory Commission (NBAC) to write a report on cloning. The report concluded that no one knew whether cloning to make a human baby was safe, and therefore human cloning should not be done. The panel feared that a baby might be born with severe birth defects. There was also concern that the process was so inefficient it would take literally hundreds of eggs to get a single successful pregnancy. NBAC called for another committee to revisit the issue in five years time.

In 2002, President Bush's Council on Bioethics wrote a report arguing that reproductive cloning should be banned, but left the door open to allowing research/therapeutic cloning. The council seemed headed toward a recommendation to approve research cloning before last-minute politicking by cloning opponents blocked that move. Most governments across the world have also taken the position that cloning to create a human being should be banned.

President Bush has expressed his opposition to any kind of human embryo cloning on numerous occasions.

Opponents of research/therapeutic cloning object on both a practical and an ethical basis. Practical objections include the theoretical impossibility of ensuring that a clone created for research purposes will not subsequently "get away" and be implanted into a woman to grow into a human baby. Those who cite ethical objections recoil at the idea that a potential life is being created solely for the purpose of supplying material for medicine or research.

audio icon Listen to an NPR report on the decisions reached by President Bush's bioethics council.

Read the president's council July 2002 report.

Read the 1997 report by President Clinton's council.

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What are some of the ethical issues involved?

Part of the controversy picks up at the point when cloning -- if ever -- is made safe. That possibility raises countless questions, with few obvious answers.

Ethicists say family dynamics would be fraught with problems. Consider even the most innocuous case where an infertile couple who seeks a child has one by cloning the wife. What happens to family dynamics when the daughter grows into the spitting image of the woman the father fell in love with?

Or what if the father is cloned and the parents subsequently divorce? Would the mother feel differently toward the clone of daddy if she can't stand the sight of daddy anymore?

And what about the clone as an individual? Is it reasonable to expect he or she will be treated as simply another child? There's also the concern that clones would spend their lives burdened by the knowledge that they're not an original, that they're just a copy of someone else's genetic makeup.

Others would argue that a clone is more than the sum of its genes; that experiences, starting in the womb and building throughout life, would shape what kind of person a clone grows into. For instance, identical twins have identical genes, and while they may be similar, they are distinct human beings.

As for arguments that cloning will create difficult family relationships, some say society has successfully dealt with those kinds of problems already. Children have been born using donated eggs, donated sperm and surrogate mothers, and those children are all accepted into society.

On a broader level, there are concerns that cloning would become another divisive class issue, with only the wealthy able to afford the procedure. Are there long-term consequences to manipulating human reproduction? There's also the shadow of eugenics: Cloning might be used to select -- or reject -- certain traits, depending on a society's preferences. In India and China, abortions have been used for decades to select against daughters, to the point where census reports have found women are in short supply in some communities.

audio icon Hear more about the ethics involved in an NPR interview with Leon Kass, chair of the President's Council on Bioethics.

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Is human cloning banned in the United States?

In the United States, there are no federal laws specifically regarding human cloning.

There is a prohibition on spending federal money on human embryo research of any kind, and President Bush has interpreted that to extend to human embryonic stem cells, except in the case of embryonic stem cells that were created before Aug. 9, 2001. There are about six-dozen stem-cell lines eligible for study with federal money. Private funds, however, can be used to create embryos.

Federal legislation has stalled because of political views on abortion and research. Some anti-abortion forces would like to see all forms of cloning banned. They have been unwilling to see a partial ban that would allow therapeutic cloning, because they regard embryos as humans, making it unethical to experiment on them. The science lobby backs a partial ban that would prohibit reproductive cloning, but allows therapeutic cloning.

The Food and Drug Administration has asserted its authority over anyone who attempts to make a human baby via cloning, but legal experts think FDA's authority could be challenged.

audio icon Listen to an NPR report on scientists' views about the Bush administration's restrictions on stem cell research.

Read a transcript of Bush's Aug. 9, 2001 announcement to allow limited federal funding for stem cell research.

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What countries have banned human cloning?

More than 30 countries have formally banned human cloning for reproductive purposes. Several European countries, including France, Germany and Switzerland, have banned the creation of cloned human embryos for reproductive or therapeutic purposes. England, Singapore, Sweden, China and Israel allow cloning for research, but prohibit it for reproduction.

Read positions other countries are taking at the Global Lawyers and Physicians for Human Rights Web site.

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