Although some experts think cloning can save many species that would otherwise disappear, others argue that cloning produces a population of genetically identical individuals that lack the genetic variability necessary for species survival.
Some people also have expressed interest in having their deceased pets cloned in the hope of getting a similar animal to replace the dead one.
But as shown by Cc the cloned cat, a clone may not turn out exactly like the original pet whose DNA was used to make the clone.
Reproductive cloning is a very inefficient technique and most cloned animal embryos cannot develop into healthy individuals. For instance, Dolly was the only clone to be born live out of a total of cloned embryos. This very low efficiency, combined with safety concerns, presents a serious obstacle to the application of reproductive cloning. Researchers have observed some adverse health effects in sheep and other mammals that have been cloned. These include an increase in birth size and a variety of defects in vital organs, such as the liver, brain and heart.
Other consequences include premature aging and problems with the immune system. Another potential problem centers on the relative age of the cloned cell's chromosomes. As cells go through their normal rounds of division, the tips of the chromosomes, called telomeres, shrink. Over time, the telomeres become so short that the cell can no longer divide and, consequently, the cell dies. This is part of the natural aging process that seems to happen in all cell types.
As a consequence, clones created from a cell taken from an adult might have chromosomes that are already shorter than normal, which may condemn the clones' cells to a shorter life span. Indeed, Dolly, who was cloned from the cell of a 6-year-old sheep, had chromosomes that were shorter than those of other sheep her age. Dolly died when she was six years old, about half the average sheep's year lifespan. Therapeutic cloning involves creating a cloned embryo for the sole purpose of producing embryonic stem cells with the same DNA as the donor cell.
These stem cells can be used in experiments aimed at understanding disease and developing new treatments for disease. To date, there is no evidence that human embryos have been produced for therapeutic cloning.
The richest source of embryonic stem cells is tissue formed during the first five days after the egg has started to divide. At this stage of development, called the blastocyst, the embryo consists of a cluster of about cells that can become any cell type.
Stem cells are harvested from cloned embryos at this stage of development, resulting in destruction of the embryo while it is still in the test tube. Researchers hope to use embryonic stem cells, which have the unique ability to generate virtually all types of cells in an organism, to grow healthy tissues in the laboratory that can be used replace injured or diseased tissues.
In addition, it may be possible to learn more about the molecular causes of disease by studying embryonic stem cell lines from cloned embryos derived from the cells of animals or humans with different diseases. Finally, differentiated tissues derived from ES cells are excellent tools to test new therapeutic drugs. Many researchers think it is worthwhile to explore the use of embryonic stem cells as a path for treating human diseases.
However, some experts are concerned about the striking similarities between stem cells and cancer cells. Both cell types have the ability to proliferate indefinitely and some studies show that after 60 cycles of cell division, stem cells can accumulate mutations that could lead to cancer. Therefore, the relationship between stem cells and cancer cells needs to be more clearly understood if stem cells are to be used to treat human disease.
Gene cloning is a carefully regulated technique that is largely accepted today and used routinely in many labs worldwide. However, both reproductive and therapeutic cloning raise important ethical issues, especially as related to the potential use of these techniques in humans.
Reproductive cloning would present the potential of creating a human that is genetically identical to another person who has previously existed or who still exists. This may conflict with long-standing religious and societal values about human dignity, possibly infringing upon principles of individual freedom, identity and autonomy.
However, some argue that reproductive cloning could help sterile couples fulfill their dream of parenthood. Others see human cloning as a way to avoid passing on a deleterious gene that runs in the family without having to undergo embryo screening or embryo selection.
Therapeutic cloning, while offering the potential for treating humans suffering from disease or injury, would require the destruction of human embryos in the test tube. Consequently, opponents argue that using this technique to collect embryonic stem cells is wrong, regardless of whether such cells are used to benefit sick or injured people. Cloning Fact Sheet. Do clones ever occur naturally? What are the types of artificial cloning? Human Cloning. Scientists successfully clone monkeys; are humans up next?
Aggregated News. Animal Biotechnologies. Born This Week: Dolly the Sheep. By Pete Shanks Biopolitical Times. A Star is Born On July 5, , the most famous individual sheep in history was born: Dolly, the first mammal cloned from an adult cell.
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Inui, A. Obesity — a chronic health problem in cloned mice? Trends Pharmacol. Download references. We each acknowledge discussions with colleagues during the development of these ideas and are grateful for funding from the governments, charities and commercial agencies that are acknowledged in our research papers.
We apologize to colleagues whose work we have been unable to cite, but limitations of space in many cases limit citations to reviews rather than the source papers. Jane E. Taylor, Paul A.
De Sousa, Tim J. You can also search for this author in PubMed Google Scholar. Correspondence to Susan M. Beckwith—Wiedeman syndrome. Somatic cell nuclear transfer cloning efficiency. The process by which the nucleus from an adult cell is transferred into a previously enucleated cell; the reconstructed oocyte is activated, which initiates subsequent development.
Literally means 'outside conventional genetics'; this term describes any heritable change in gene expression that is not caused by a change in DNA sequence.
A preimplantation embryo that contains a fluid-filled cavity blastocoel , a focal cluster of cells from which the embryo will develop inner cell mass and peripheral trophoblast cells. A small group of cells that are present in the blastocyst, which comprise undifferentiated cells. The state of those mechanisms that regulate gene expression and are transmitted to daughter cells. The epigenetic marking of a gene on the basis of parental origin, which results in monoallelic expression.
A short repeat sequence of DNA at the end of chromosomes, which both protects and ensures the complete replication of chromosome ends. A somatic cell that is found in the ovarian follicles, which supports oocyte growth, maturation and ovulation. Reprints and Permissions. Human cloning: can it be made safe?. Nat Rev Genet 4, — Download citation. Issue Date : 01 November Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article.
Provided by the Springer Nature SharedIt content-sharing initiative. Molecular Biology Reports Stem Cell Reviews and Reports Biomedical Microdevices Nature Reports Stem Cells Advanced search. Skip to main content Thank you for visiting nature. Key Points Somatic cell nuclear transfer SCNT is the process whereby the nucleus from an adult cell is transferred into a previously enucleated oocyte, followed by oocyte activation and the ultimate production of a clone of the original source adult cell.
Abstract There are continued claims of attempts to clone humans using nuclear transfer, despite the serious problems that have been encountered in cloning other mammals. Access through your institution. Buy or subscribe. Rent or Buy article Get time limited or full article access on ReadCube. Figure 1: Overview of the somatic cell nuclear-transfer procedure. Figure 2: Overview of clone development showing the factors that contribute to clone failure.
Figure 3: Flow diagram of a proposed experimental approach to understanding clone failure. References 1 Wilmut, I.
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