Table of Contents > Genomics > Cloning Print

Cloning

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Related terms
Background
Methods
Research
Implications
Limitations
Safety
Future research
Author information
Bibliography

Related Terms
  • Blastocyst, cell division, chromosome, clone, DNA, development, duplication, embryo, nucleus, reproductive cloning, replication, somatic cell nuclear transfer, stem cell research, therapeutic cloning.

Background
  • Cloning is a technique in which a researcher removes DNA (deoxyribonucleic acid) from the egg of an organism, and replaces it with new DNA. The egg with the new DNA can then be used to produce an organism that contains the new DNA in all the cells of its body or to produce embryonic stem cells. Embryonic stem cells are a type of cell that has the potential to develop into any type of tissue or organ, such as blood, skin, or liver.
  • DNA is located in a compartment of the cell called the nucleus and is packaged in structures called chromosomes. Human cells contain 46 chromosomes, and each chromosome has hundreds of genes. Genes contain the instructions for making the proteins that serve various functions in the human body. Variation in DNA is responsible for many of the differences seen among individuals, for example, height and eye color.
  • When researchers perform cloning, their goal is to produce an organism, tissue, or cell that carries the same DNA as an original donor cell. For example, researchers may use cloning to help repopulate endangered species. DNA from a specific organism can be used to produce genetically identical organisms. Researchers also hope to use cloning to treat human disease. DNA from a sick individual may be used to grow a new organ or tissue to help treat that individual. For example, new brain cells could be grown to treat patients with degenerative nervous system diseases.
  • Although cloning has the potential to help people, it raises ethical concerns. For example, many people believe it is not right to create a clone of a human being. Also, a human embryo is destroyed when cloning is used to generate human embryonic stem cells. Due to ethical concerns, some people do not support stem cell research that involves cloning or embryonic stem cells and believe it should be banned.

Methods
  • Somatic cell nuclear transfer: To perform cloning, researchers commonly use a method called somatic cell nuclear transfer. In somatic cell nuclear transfer, the nucleus of a somatic cell, which is any cell type in the body except for reproductive cells, such as egg or sperm cells, is transferred into an unfertilized egg that has had its nucleus removed. The nucleus is a compartment of the cell that contains chromosomes and DNA. A human egg cell nucleus contains only 23 chromosomes (i.e., not the entire paired set), but a human somatic cell nucleus contains 46. Skin cells are a type of somatic cell type commonly used for cloning.
  • To remove the nucleus from an egg cell and replace it with the nucleus of a somatic cell, scientists observe the cells under a microscope and carefully remove the egg nucleus using fine glass needles. They may then use an electrical pulse to cause the somatic cell and the egg cell to fuse into one cell, which will contain the somatic cell nucleus. Alternatively, researchers may inject the somatic cell nucleus into the egg cell using glass needles.
  • After replacing the egg nucleus with a somatic nucleus, the cell divides several times until an embryo of about 100 cells, a blastocyst, has formed. Researchers still understand very little about the process through which the somatic cell DNA is reprogrammed by the egg cell and how it is able to control these cell divisions to produce a blastocyst.
  • Therapeutic cloning: Researchers may then isolate embryonic stem cells from the blastocyst and continue to grow and study the embryonic stem cells in the laboratory. This type of cloning is called therapeutic cloning. In the future, researchers hope to be able to use therapeutic cloning to treat patients with medical conditions such as degenerative nervous system diseases.
  • Reproductive cloning: Alternatively, researchers may implant the entire blastocyst into a surrogate mother, in whom the blastocyst will continue to grow and develop as a fetus. If development of the cloned organism occurs normally, the surrogate mother will then give birth to a healthy infant. This type of cloning is called reproductive cloning. Reproductive cloning generally is not being studied as a treatment for disease.

Research
  • Produce organisms: Cloning may be used to make identical copies of a particular organism. This is called reproductive cloning. Researchers have been successful in creating clones of many different types of species, including sheep, mice, cats, and fish. Cloning has been used to make human embryonic stem cells, but a fully developed cloned embryo has never been produced.
  • Cloning may also be used to help repopulate some endangered species. For example, an endangered species of ox called the Banteng has been successfully cloned.
  • Cloned animals may be used for some research purposes. Because cloned animals all have the same DNA and should all have a uniform response to a specific drug, they may be used to test new drugs.
  • Cloning may also be used to genetically modify animals for human benefit. For example, organs from some animals, such as pigs, may be used for an organ transplant by humans who have failing organs. However, animal organs may be rejected by the human body when transplanted. Researchers have recently generated genetically modified pigs through cloning. These pigs have alterations in several genes that may make their organs less likely to be rejected when transplanted into a human body.
  • Obtain stem cells: Stem cells are usually obtained from an embryo. Cloning that is used to make embryos for the purpose of obtaining embryonic stem cells is called therapeutic cloning. Because stem cells play a central role in biology, researchers may study these stem cells to learn more about how human development occurs. For example, researchers may investigate which genes are turned on or off in a stem cell.

Implications
  • Treat diseases: Researchers hope to use cloning to treat human diseases. If a somatic cell from a diseased individual is obtained, it could be used to make embryonic stem cell lines from that individual, and eventually to grow a new organ or tissue to help treat that individual. For example, new brain cells could be grown from embryonic stem cells to treat patients with degenerative nervous system diseases. Organs or tissues that contain a patient's own DNA would be less likely to be rejected by the body than organs or tissues donated from another person. This research is only its early stages; however, and has not yet progressed to the point where it is being used to treat humans. One challenge is to learn how to make embryonic stem cells develop into a specific type of tissue, for example, brain cells.
  • Researchers may also be able to learn more about certain diseases using cloning. By studying embryonic stem cells that were made from an animal or human with a specific disease and comparing them to stem cells from a healthy individual, scientists may be able to learn more about what causes that disease. For example, scientists may be able to learn whether specific genes are turned on or off in the cells from the diseased organism. Ultimately, this may lead to the development of new drugs to treat the disease.
  • Study development: Researchers may use cloning to study development in model organisms, such as mice. To study development, researchers may genetically modify DNA from a mouse so that a gene they are interested in is deleted or replaced. They can then use this genetically modified DNA for reproductive cloning to create mice that have this genetic modification. By observing how the development of these modified mice differs from normal development, they may learn more about the function of the modified gene.

Limitations
  • Although cloning has the potential to help many people, it is controversial because it raises ethical concerns. For example, many people believe it is not right to create a clone of a human being. Also, a human embryo is destroyed when using cloning to generate human embryonic stem cells. Due to ethical concerns, many people do not support stem cell research that involves cloning or embryonic stem cells and believe it should be banned.

Safety




Future research
  • In the future, researchers hope to obtain embryonic stem cells without destroying an embryo. Current research in this area focuses on studying the genes required to make an embryonic stem cell. By identifying genes required for embryonic stem cell function and by increasing the production of these genes in other cell types, researchers hope to turn other cells into embryonic stem cells in the laboratory.

Author information
  • This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

Bibliography
  1. Byrne JA, Pedersen DA, Clepper LL, et al. Producing primate embryonic stem cells by somatic cell nuclear transfer. Nature. 2007 Nov 22;450(7169):497-502.
  2. Hall VJ, Stojkovic P, Stojkovic M, et al. Using therapeutic cloning to fight human disease: a conundrum or reality. Stem Cells. 2006 Jul;24(7):1628-37.
  3. Han Z, Vandevoort CA, Latham KE, et al. Therapeutic cloning: status and prospects. Curr Opin Mol Ther. 2007 Aug;9(4):392-7.
  4. National Human Genome Research Institute. .
  5. Natural Standard: The Authority on Integrative Medicine. .
  6. Oak Ridge National Lab. .
  7. Phelps CJ, Koike C, Vaught TD, et al. Production of alpha 1,3-galactosyltransferase-deficient pigs. Science. 2003 Jan 17;299(5605):411-4.
  8. University of Utah Genetic Science Learning Center. .
  9. Wakayama T, Tabar V, Rodriguez I, et al. Differentiation of embryonic stem cell lines generated from adult somatic cells by nuclear transfer. Science. 2001 Apr 27;292(5517):740-3.

Copyright © 2011 Natural Standard (www.naturalstandard.com)


The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.

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