Chapter 3 Cloning

 

by Donna M. Brinton, Christine Holten, and Jodi L. Nooyen

Background | Classroom Applications | Internet Resources | Appendices

Background

Ever since Gregor Mendel discovered how to manipulate traits in plants, people have been able to clone plant life relatively simply—even in their own gardens. However, cloning animals was only possible in the imagination of science fiction writers. Thus, the world was shocked in 1997 to learn that scientists at the Roslin Institute in Edinburgh, Scotland had cloned a Finn Dorset sheep named Dolly. The success of this experiment has opened the door to cloning other animal life. In the years following the cloning of Dolly, scientists successfully cloned mice, pigs, cows, chickens, and even more exotic animals such as the endangered gaur, a humpbacked relative of a cow from Southeast Asia. This type of research could bring great benefits to humans; but it also raises ethical and moral concerns.

Some of the questions this chapter explores include:

• What is cloning?
  
  
• How is cloning different from previous methods used to breed plants and animals?
  
  
• What process was used to clone Dolly the sheep?
  
  
• How might we use this new technology?
  
  
• What are the benefits and potential drawbacks of cloning?

This chapter will give students a basic understanding of how cloning works and how it is currently being applied. It will also examine future uses of cloning, including the possibility of cloning humans. Teachers can use the lesson plans and materials to help students gain a basic understanding of these fundamental concepts and a command of the vocabulary necessary to discuss them.

Frequently Asked Questions about Cloning

1. What is cloning?
Unlike sexual reproduction, which combines the genetic material of two individuals, cloning involves creating a new organism or individual by copying the genetic material of only one original organism. Cloning can be done in two ways: (1) fission, a cell dividing into two cells or (2) mitosis, the nucleus of a cell dividing with each chromosome splitting into two.

2. Which organisms are the most frequently cloned today?
Plants. For centuries, people have taken roots or stems of plants in order to make genetically identical copies. Usually this is done by choosing the best plant (for example, the most decorative or unusual), cutting a root or branch from it, and placing that cutting in water or soil. The cells will then divide and double in size every six weeks until the cutting develops roots. At this point, it is ready to be planted. It will then grow into an exact copy of the parent plant.

3. What is the most famous case of cloning?
Dolly the sheep. In 1997, scientists successfully cloned an adult mammal, the Finn Dorset sheep Dolly. Overnight, she became the most famous animal in the world. Although the technology used to clone Dolly was experimental at the time, it has proven useful in the years since she first appeared. Now, scientists are cloning cows, chickens, and pigs. They are also able to produce clones from animal fetal cells quite easily.

4. What is the difference between cloning and breeding?
For years, specialists in animal husbandry have been able to breed characteristics in and out of animals, thereby creating improved animal breeds. For example, dog breeders have been able to control the genetic makeup of species to obtain certain physical characteristics such as eye or fur color, size, or special abilities such as speed or herding. Breeding, however, is different from cloning in two ways. First, it can only be done with embryonic cells (cells that result in the production of offspring). Second, breeding does not produce an exact replica. Breeders can calculate the probability of obtaining a certain trait, but to actually obtain this trait they may have to try several times. With cloning, scientists can choose any healthy individual whose characteristics they wish to clone and create an exact copy by using cells from that animal.

5. How does cloning work?
In its most basic form, cloning involves three steps. In the first step, scientists take cells from an individual whose characteristics they want to copy. They place these cells, which are called donor cells, into a liquid culture. This culture contains nutrients and stops the cells from dividing. In the second step, an unfertilized egg is taken from a female. Its nucleus is removed, leaving an empty egg cell. The donor cell is then placed into the empty egg. This process creates an embryo that is an exact copy of the donor and not the mother. In the final step, the embryo is put into the uterus of a female of the species and arrives into the world via the natural birth process.

6. Is cloning unnatural?
No, cloning already occurs in nature. In fact, the only way that many organisms (for example, bacteria, yeast, snails, and shrimp) can reproduce is through cloning. Mammals reproduce naturally only through sexual reproduction. Thus, only scientists working in a laboratory can clone a mammal. The problem with cloning, however, is that it does not improve the genetic makeup of a species.

7. What is the difference between an identical twin and a clone?
Both identical twins and clones consist of the exact same genetic material. But a clone cannot be considered an identical twin of the donor because it does not share the same time in the womb. Twins experience the same environmental factors before birth (such as nutrition and exposure to stress, hormones, alcohol, and drugs), which play an enormous role in their physical and mental development. The clone, on the other hand, only shares genetic material with its donor and lacks the pre-natal environmental exposure of an identical twin.

8. Could cloning be used to produce vital organs for transplant?
Hypothetically yes. The only way to do this, however, would be to reproduce the entire individual, including its organs. This practice would raise ethical questions. Time is also a problem. It would take a long time for a donor’s organs to be mature enough to be removed from the donor and used for transplant. In addition, scientists are unsure whether transplanted organs from cloning would be accepted or rejected by the recipient individual.

9. Could endangered species be saved through cloning?
Possibly. At the present time, the success of this is unlikely. It took 276 tries to clone Dolly the sheep. But if the success rate of cloning increases, it could be a way to increase the population of endangered species or animals that are difficult to breed.

10. Could extinct species be revived using cloning?
This would be more difficult. Cloning extinct animals poses two problems. First, donor cells must be taken from living organisms. Unless an extinct animal is found completely frozen (such as the wooly mammoth recently discovered in the Arctic), it would be impossible to find living cells. For example, because the fossil bones of dinosaurs contain no living cells, a dinosaur cannot be cloned. Second, current cloning technology requires a surrogate mother and an egg cell from a living female of the same species. Females normally cannot give birth to an animal from a different species. It is unlikely, for instance, that a female elephant could donate an egg cell and give birth to a wooly mammoth.

11. What are the benefits of cloning?
We are more certain of obtaining desired traits through cloning than through conventional breeding. For example, cloning could benefit crop engineering by creating foods that are more nutritious, disease free, and plentiful. Cloning could also help in the prevention and cure of diseases. For instance, the same laboratory that created Dolly the sheep is now working to create eggs that contain anticancer proteins to prevent various forms of cancer (such as fast growing forms of skin cancer). Dolly herself was cloned to produce a sheep whose milk had more proteins that are believed to help treat diseases such as emphysema, hemophilia, and cystic fibrosis.

12. What are the disadvantages of cloning?
One potential disadvantage of cloning is that “breeding” humans would become easier. While we have done this for centuries with other large animals such as race horses, cloning humans raises moral and ethical concerns. There is great potential for abuse if humans are able to design their offspring. The ability to breed in or out certain traits would raise questions of how tall or how intelligent we would want our children to be, or what color skin and eyes we would want them to have. These are questions that make us uncomfortable. In addition, it would be problematic to invest so much in changing or improving human genetic makeup because we might ignore the impact that the environment has on an individual’s development. A further problem is that clones could be misused, for example, as spare part tissues and organs or as slave labor.

Glossary

Breed: To produce (offspring); give birth or hatch.

Clone: A population of identical molecules, cells, or organisms derived from a common source. Because no genetic material is combined (as in sexual reproduction), a clone is genetically identical to the parent.

Consent: To indicate or express a willingness.

Culture: Microorganisms, tissue cells, or other living matter grown in a specially prepared nutrient medium.

Crop: Cultivated plants or agricultural produce, such as grains, vegetables, or fruit.

Cystic fibrosis: (Abbreviation CF) A hereditary disease that usually develops during early childhood and mainly affects the pancreas, respiratory system, and sweat glands. It usually results in chronic respiratory infections and impaired pancreatic function.

Dinosaur: Any of various extinct, often gigantic reptiles.

Donor: One from whom blood, tissue, or an organ is taken for use in a transfusion or transplant. (Note: can also be used as an adjective, as in “embryonic donor cells.”

Embryonic: 1. Of or relating to an embryo; 2. Of an organism prior to birth or hatching; as in “in the embryonic stage.”

Emphysema: An abnormal condition of the lungs characterized by decreased respiratory function; associated with smoking, chronic bronchitis, or old age.

Endangered: Faced with the danger of extinction: an endangered species.

Fertilize: Make fertile or productive 2. Introduce semen into (a female).

Fetal: Of, relating to, characteristic of, or being a fetus: a fertilized egg.

Fission: An asexual (non-sexual) reproductive process in which a one-cell organism divides into two or more independently maturing cells.

Fossil: A remnant or trace of an organism of a past geologic age, such as a skeleton or leaf imprint, embedded and preserved in rock.

Gaur: A large East Indian species of wild cattle. For more information: http://www.nature.ca/notebooks/english/gaur.htm

Gregor Mendel: Founder of the science of genetics (1822–1884). An Austrian monk and botanist.

Hemophilia: A genetic blood disorder in which the blood fails to clot normally. This disorder is hereditary and is due to a deficiency in or an abnormality of one of the clotting factors. Hemophilia is manifested almost exclusively in males.

Hormone: A naturally occurring substance secreted by specialized cells that affects the behavior of other cells.

Husbandry: 1.The act or practice of cultivating crops and breeding and raising livestock; agriculture. 2. The application of scientific principles to agriculture, especially to animal breeding.

Implant: 1. To put an object or a device in a person or animal via surgery.

Manipulate: To handle and move in an examination or for therapeutic purposes: manipulate a joint; manipulate the position of a fetus during delivery.

Mitosis: The entire process of cell division including division of the nucleus and the cytoplasm.

Nucleus: A large circular structure within a living cell that contains the cell's hereditary material and controls its metabolism, growth, and reproduction.

Offspring: A child; a daughter or son.

Organism: An individual life form, such as a plant or an animal; a body made up of organs or other parts that work together to carry out the various processes of life.

Protein: The principal constituent of all cells, essentially consisting of combinations of amino acids and peptide linkages.

Reject: To resist the introduction of (a transplanted organ or tissue); fail to accept as part of one's own body.

Replicate: To make an exact copy or copies of (genetic material, a cell, or an organism).

Reproduce: To generate offspring by sexual or asexual (non-sexual) means.

Roots: The usually underground portion of a plant that serves as support, draws minerals and water from the surrounding soil, and sometimes stores food.

Surrogate: One that takes the place of another; a substitute: a surrogate mother.

Trait: A genetically determined characteristic or condition: a recessive trait.

Transplant: To transfer (tissue or an organ) from one body or body part to another.

Uterus: A hollow muscular organ located in the pelvic cavity of female mammals in which the fertilized egg implants and develops. Also called a womb.

Via: 1. By way of. 2. By means of.

Vital: Necessary to the continuation of life; life-sustaining: a vital organ, vital nutrients.

Woolly mammoth: Hairy extinct mammoth common in colder portions of the northern hemisphere. For more information: http://dsc.discovery.com/convergence/landofmammoth/dispatches/dispatch.html

Womb: A hollow muscular organ located in the pelvic cavity of female mammals in which the fertilized egg implants and develops. Also called a uterus.

 

Return to Top

This site is maintained by the Bureau of Educational and Cultural Affairs, U.S. Department of State. Links to other sites should not be construed as an endorsement of the views contained therein.