Cloning

Cloning hit the news headlines in 1997 when scientists in Scotland announced they had successfully cloned a sheep, named Dolly, in 1996. Although several other animal species had been cloned in the previous 20 years, it was Dolly that caught the public's attention. Suddenly, the possibility that humans might soon be cloned jumped from the pages of science fiction stories into the mainstream press. Dolly was the first adult mammal ever cloned.

Cloning is the science of using artificial methods to create clones. A clone is a single cell, a group of cells, or an organism produced in a laboratory without sexual reproduction. In effect, the clone is an exact genetic copy of the original source, much like identical twins. There are two types of cloning. Blastomere separation, also called "twinning" after the naturally occurring process that creates identical twins, involves splitting a developing embryo soon after the egg is fertilized by sperm. The result is identical twins with DNA from both parents. The second cloning type, called nuclear transfer, is what scientists used to create Dolly. In cloning Dolly, scientists transferred genetic material from an adult female sheep to an egg in which the nucleus containing its genetic material had been removed.

Simple methods of cloning plants, such as grafting and stem cutting, have been used for more than 2,000 years. The modern era of laboratory cloning began in 1958 when the English-American plant physiologist Frederick C. Steward cloned carrot plants from mature single cells placed in a nutrient culture containing hormones, chemicals that play various and significant roles in the body.

The first cloning of animal cells occurred in 1964. In the first step of the experiment, biologist John B. Gurdon destroyed with ultraviolet light the genetic information stored in a group of unfertilized toad eggs. He then removed the nuclei (the part of an animal cell that contains the genes) from intestinal cells of toad tadpoles and injected them into those eggs. When the eggs were incubated (placed in an environment that promotes growth and development), Gurdon found that 1–2% of the eggs developed into fertile, adult toads.

The first successful cloning of mammals was achieved nearly 20 years later. Scientists in both Switzerland and the United States successfully cloned mice using a method similar to that of Gurdon. However, the Swiss and American methods required one extra step. After the nuclei were taken from the embryos of one type of mouse, they were transferred into the embryos of another type of mouse. The second type of mouse served as a substitute mother that went through the birthing process to create the cloned mice. The cloning of cattle livestock was achieved in 1988 when embryos from cows were transplanted to unfertilized cow eggs whose own nuclei had been removed.

Since Dolly, the pace and scope of cloning mammals has greatly intensified. In February 2002, scientists at Texas A&M University announced they had cloned a cat, the first cloning of a common domestic pet. Named "CC" (for carbon copy or copycat), the cat is an exact genetic duplicate of a two–year–old calico cat. Scientists cloned CC in December 2001 using the nuclear transfer method. In April 2002, a team of French scientists announced they had cloned rabbits using the nuclear transfer process. Out of hundreds of embryos used in the experiment, six rabbits were produced, four that developed normally and two that died. Two of the cloned rabbits mated naturally and produced separate litters of seven and eight babies

The first human embryos were cloned in 1993 using the blastomere technique that placed individual embryonic cells (blastomeres) in a nutrient culture where the cells then divided into 48 new embryos. These experiments were conducted as part of some studies on in vitro (out of the body) fertilization aimed at developing fertilized eggs in test tubes that could then be implanted into the wombs of women having difficulty becoming pregnant. However, these fertilized eggs did not develop to a stage that was suitable for transplantation into a human uterus.

Research into cloning humans also picked up greatly following the success of Dolly. An Italian physician said in April 2002 that a woman was pregnant with what would be the world's first cloned human baby. The doctor, Severino Antinori, operates a fertility clinic near the Vatican in Rome. In March 2002, a Chinese researcher said she had cloned a human embryo to the blastocyst stage, the point at which stem cells can be harvested. Scientists in several other countries also are believed conducting human cloning experiments.

The cloning of cells promises to produce many benefits in farming, medicine, and basic research. In farming, the goal is to clone plants that contain specific traits that make them superior to naturally occurring plants. For example, field tests have been conducted using clones of plants whose genes have been altered in the laboratory by genetic engineering to produce resistance to insects, viruses, and bacteria. New strains of plants resulting from the cloning of specific traits have led to fruits and vegetables with improved nutritional qualities, longer shelf lives, and new strains of plants that can grow in poor soil or even under water.

A cloning technique known as twinning could induce livestock to give birth to twins or even triplets, thus reducing the amount of feed needed to produce meat. Cloning also holds promise for saving certain rare breeds of animals from extinction , such as the giant panda .

In medicine, gene cloning has been used to produce vaccines and hormones. Cloning techniques have already led to the inexpensive production of the hormone insulin for treating diabetes and of growth hormones for children who do not produce enough hormones for normal growth. The use of monoclonal antibodies in disease treatment and research involves combining two different kinds of cells (such as mouse and human cancer cells) to produce large quantities of specific antibodies. These antibodies are produced by the immune system to fight off disease. When injected into the blood stream, the cloned antibodies seek out and attack disease–causing cells anywhere in the body.

Despite the benefits of cloning and its many promising avenues of research, certain moral, religious, and ethical questions concerning the possible abuse of cloning have been raised. At the heart of these questions is the idea of humans tampering with life in a way that could harm society, either morally or in a real physical sense. Some people object to cloning because it allows scientists to "act like God" in manipulating living organisms.

The cloning of Dolly and the fact that some scientists are attempting to clone humans raised the debate over this practice to an entirely new level. A person could choose to make two or 10 or 100 copies of himself or herself by the same techniques used with Dolly. This realization has stirred an active debate about the morality of cloning humans. Some people see benefits from the practice, such as providing a way for parents to produce a new child to replace one dying of a terminal disease. Other people worry about humans taking into their own hands the future of the human race.

Another controversial aspect of cloning deals not with the future but the past. Could Abraham Lincoln or Albert Einstein be recreated using DNA from a bone, hair, or tissue sample? If so, perplexing questions arise about whether this is morally or ethically acceptable? Some scientists say that while it might be possible to do this, the clone might be identical in appearance and in some traits, it would not have the same personality as the original Lincoln. This is because Lincoln, like all people, was greatly shaped from birth by his environment and personal experiences in addition to his genetic coding. Although a duplicate of her mother, CC, the cloned calico cat, has a different color pattern on her fur. This is because environmental factors strongly influence her development in the womb.

Also, since the movie "Jurassic Park" was released in 1993, there has been considerable public discussion about the possibility of cloning dinosaurs and other prehistoric or extinct species. In 1999, the Australian Museum in Sydney, Australia , announced scientists were attempting to clone a thylacine (a meat–eating marsupial related to kangaroos and opossums). It has been extinct since 1932 but the museum has the body of a baby thylacine that has been preserved for 136 years. The problem is that today's cloning techniques are possible only with living tissue. Even the head of the project has doubts, saying the chance of cloning a living thylacine is 30% over the next 200 years.

[Ken R. Wells ]

RESOURCES

BOOKS

Cefrey, Holly. Cloning and Genetic Engineering (Life in the Future). New York: Children's Press, 2002.

Pence, Gregory E. Who's Afraid of Human Cloning? Lanham, MD: Rowman & Littlefield Publishers, 1998.

PERIODICALS

Gibbs, Nancy. "Baby, It–s You! And You, And You..." Time (Feb. 11, 2001).

Hobson, Katherine. "Pets of the Future." U.S. News & World Report (March 11, 2002): p. 46.

Masibay, Kim Y. "Copy Cat." Science World (March 25, 2002): p. 6–7.

McGovern, Celeste. "Brave New World." The Report Newsmagazine (April 29, 2002).

Pistoi, Sergio. "Father of the Impossible Children." Scientific American (April 2002): p. 38–40.

"The Clone Wars.' Business Week (March 25, 2002): p. 94.

Weidensaul, Scott. "Raising the Dead." Audubon (May–June 2002): p.
58–67.

ORGANIZATIONS

The Human Cloning Foundation, <http://www.humancloning.org>

Society for Developmental Biology, 9650 Rockville Pike, Bethesda, MD USA 20814 301–571–0647, Fax: 301–571–5704, Email: [email protected], <http://www.sdb.bio.purdue.edu>