However, the company responsible, Advanced Cell Technology (ACT), says it is not creating embryos in order to make exact copies of individuals. Rather, ACT hopes to use the embryos to harvest precious "stem cells" — cells that, in theory, can ultimately grow into any kind of cell in the body (such as those found in liver tissue and brain tissue). These cells could be used to generate new organs or cell clusters to treat patients with failing organs or degenerative diseases. Advanced Cell Technology lists people with cancer, HIV, diabetes, and Parkinson's disease as some of the potential beneficiaries of their work. In the case of transplant patients, for example, organs made from exact copies of an individual's own cells — custom-made organs, so to speak — would not be rejected.

This "human therapeutic cloning," as the practice is being called, sounds like the medicine of science fiction. And it is still in its earliest phase of development, with only modest success rates being reported by ACT. (All of the embryos they generated actually died — none grew beyond the six-cell stage.) Even so, detractors fear that these preliminary efforts could set a chain of scientific developments in motion. The thinking is that by allowing any kind of cloning of human embryos, it is then not such an enormous leap to apply the same techniques to making copies of people.

• Read CNN's evaluation of the recent developments in the article, "Cloning Work Bodes Progress."

Cloning is an evolving science that frequently makes the news because of the complex ethical questions it raises. The latest developments provide an interesting context for you to discuss with your students the practice of cloning, the basic science involved, and some of cloning's applications.

What is Cloning?
A clone is an individual organism grown from a single body cell of its parent, making it a genetic duplicate of the parent. To simplify a complex process, here are the major steps in cloning a mammal:

(1) Scientists collect an egg (an oocyte) from a female of the species that will be used as the surrogate mother. This could be the same species as the one being cloned (e.g. a cow egg used for a cow) or a different species (e.g. using a black bear egg to clone a panda).

(2) They suck the nucleus out of the original egg, removing all genetic code.

(3) They take a skin cell from the organism to be cloned and either insert that cell into the empty egg or place them together.

(4) They apply a small electrical pulse, which fuses the skin cell with the empty egg, effectively transferring the nucleus from the skin cell to the empty egg and forming a single new egg. A second electrical pulse causes this new egg to start dividing.

(5) Once the egg has divided into a number of cells, this now growing embryo is implanted into the uterus of a surrogate mother.

(6) If all goes according to plan, at the end of the gestation period, a clone is born.

The success rate of these techniques is small, as recently published figures from ACT experiments show: 500 cloned embryos were implanted into 250 cows, but only 110 resulted in pregnancy. Some of the pregnancies were not carried to term, and many calves died at birth or soon afterwards. In the end, 24 apparently healthy animals were produced.

• Read New Scientist magazine's report on these cow clones, "Investigation Claims Clones Are Completely Normal."

Last year, scientists attempted to clone a gaur, an endangered Asian ox. They implanted the cloned gaur embryo in a cow, which gave birth in January of this year. The baby gaur, which was named Noah, was healthy enough to stand unaided. But the calf caught a common infection and died of dysentery within 48 hours of birth.

Many scientists believe that cloning could help build up populations of species like the gaur that are on the verge of extinction. Other scientists worry that the public will see cloning as an "easy solution" and will not be encouraged to conserve wildlife habitats. Also, cloned animals tend to be significantly larger at birth than normal, or they often have enlarged organs, heart problems, or poor immune systems.

• Students can find out what happened to Noah, the cloned gaur, in the CNN.com article, "First cloned endangered species dies 2 days after birth."
• Just before Noah was born, some of the scientists involved wrote an article in defense of using cloning to save endangered species. Read "Cloning Noah's Ark" online in Scientific American magazine.

In July 1999, a group of scientists and ethicists decided to begin immediately an effort to revive the extinct Huia, a bird of cultural importance to New Zealand's indigenous population, the Maori. Experts expect that the actual cloning will take several years.

• Students can find more information in the ENN.com article, "Cloning of extinct Huia bird approved."

• Middle school students can explore the Principles of Genetics with a collection of Middle School Science Gateways activities.
• High school students can investigate Genetic Engineering with this Biology Gateways activity.
• The activities on Molecular Biology (DNA) in Biology Explorer take the concepts further. Of special interest here is the activity on mapping DNA, an endeavor central to cloning. There is also an inquiry into the human genome database.

Give students the following statistics:

(1) There are approximately 1,000 pandas in the wild in China and 140 pandas in zoos and breeding centers around the world.

(2) The gestation period of a panda is 17-23 weeks long.

(3) At present, scientists fertilize about 400 eggs for every 10 that they successfully implant in a mammal species.

(4) About 10% of the implanted embryos (i.e., one creature) can be expected to be born as a live offspring.

(5) Only a small number of the offspring will actually survive.

Ask students:

• Given today's technology, approximately how many panda eggs do scientists need to begin the cloning process, if the goal is to double the number of pandas in the world?
• Estimating that only about 30% of the living pandas are females capable of serving as surrogate mothers for the cloned embryos, about how long would it take to double the panda population?

• If scientists want to revive an extinct species but they only have DNA samples from a male of that species, can they build a self-sustaining species?
• What would happen to the species' gene pool if all the individuals were cloned from just a few parents?
• What problems might be encountered when reintroducing species that have become extinct?

• Conceiving a Clone: This Thinkquest site explores the science and history of the cloning process and offers animations illustrating the concepts. It also provides interactive sections where students can create a clone and participate in a questionnaire.
• Genetic Engineering and Cloning: Another Thinkquest site on cloning covers the science and history of the process, offers students a chance to debate the ethical issues, and provides games to reinforce concepts.
• The Making of Dolly: Time magazine presents a multimedia primer on cloning.

2. If you want to hold a class discussion on the ethical issues raised by cloning, especially human cloning, visit the following Web sites:

• Cloning and Human Infertility: Some believe that, despite claims to the contrary, scientists at Advanced Cell Technology Inc. are doing the work for those who really do want to make exact copies of humans. American fertility specialist Panos Zavos and Italian embryologist Severino Antinori caused an uproar when they announced their plan to use cloning as a solution to fertility problems. Read about Antinori in this BBC article.
• Ethics of Human Cloning: Students can read this transcript of a CNN online discussion forum with Dr. Jeffrey Kahn, Director of the Center of Bioethics at the University of Minnesota. The discussion took place last week, on November 27.
• Human Cloning: The Terrible Odds: In this article from BBC News, ethicist Dr. Donald Bruce looks at the key arguments against allowing human cloning for reproductive purposes.
• Human Cloning Foundation: The official site in favor of human cloning presents articles, interviews, and discussions about the perceived benefits of human cloning.

3. Further applications of cloning worthy of investigation are in the agricultural world.

• "Carbon & Copy": These are the names of two cloned cattle. Prize cattle are being cloned in an effort to preserve (or propagate) their "superior genes." Students can get the industry's perspective at this Web site as they learn about the methods used by Infigen, one of the companies doing animal cloning.
• Clone Farm: There is talk of production lines for chicken clones. Students can find out more in this New Scientist article.