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FIGURE 2 Nuclear Transplantation to Produce Stem Cells Unlike reproductive cloning, the creation of embryonic stem cells by nuclear transplantation does not involve implantation of a preimplantation embryo, or blastocyst, in a uterus.
Some confusion arises because in both cases researchers would use nuclear transplantation, which is an initial step in the successful procedures used to clone animals—beginning with the sheep Dolly and including several other mammals since then.
Thus, nuclear transplantation accurately describes the process. For both reproductive cloning and stem cell production, a reconstructed egg cell produced by nuclear transplantation is stimulated to cause it to begin dividing.
If that is successful, several sequential cell divisions can give rise to the preimplantation embryo known as a blastocyst that is composed of cells see Figure 2. It is at this stage that the procedures used for reproductive cloning and for nuclear transplantation to produce stem cells become entirely different.
In reproductive cloning, a blastocyst formed by the nuclear transplantation procedure is implanted in a uterus, where it begins the process of forming a fetus. Although these clones will be physically very similar, the animals will not be physically or behaviorally identical, because of various factors, including their different uterine and postnatal environments and experiences.
In nuclear transplantation to produce stem cells, cells are isolated from the blastocyst days after the procedure, and the cells are used to make a stem cell line for further study and clinical applications.
Neither the blastocyst nor the stem cells are ever placed into a uterus. Moreover, as described in Chapter 2human stem cells do not themselves have the capacity to form a fetus or a newborn animal.
What are the implications of doing so? Of not doing so? None of the An introduction to the biological aspects of the true human cloning summarized in the preceding section that support the panel's conclusions regarding a ban on human reproductive cloning would support a ban on the use of the nuclear transplantation technology to produce stem cells.
A recent report prepared by a different committee of the National Academies has emphasized that there is a great potential for studies on stem cells isolated through nuclear transplantation to increase the understanding and potential treatment of various diseases and debilitating disorders, as well as fundamental biomedical knowledge.
The necessary research would entail transfer of human somatic cell nuclei into enucleated human eggs for the purpose of deriving blastocysts and embryonic stem cells and stem cell lines; there would be no implantation in a uterus.
Some have expressed concern that this research might nevertheless be misdirected to human reproductive cloning. If our recommendation for a legally enforceable ban is adopted, then any attempts at implantation that might lead to the development and birth of a newborn would be criminalized.
The committee that produced the report from the National Academies entitled Stem Cells and the Future of Regenerative Medicine considered a wide range of views on the ethical and societal issues involved in the production of human embryonic stem cells—including nuclear transplantation technology [ 2 ].
After carefully considering all sides of the issue, that committee produced the following conclusion and recommendation concerning this technology: Regenerative medicine is likely to involve the implantation of new tissue in patients with damaged or diseased organs.
A substantial obstacle to the success of transplantation of any cells, including stem cells and their derivatives, is the immunemediated rejection of foreign tissue by the recipient's body.
In current stem cell transplantation procedures with bone marrow and blood, success hinges on obtaining a close match between donor and recipient tissues and on the use of immunosuppressive drugs, which often have severe and potentially life-threatening side effects. To ensure that stem cell-based therapies can be broadly applicable for many conditions and people, new means of overcoming the problem of tissue rejection must be found.
Although ethically controversial, the somatic cell nuclear transfer technique promises to have that advantage. Other options for this purpose include genetic manipulation of the stem cells and the development of a very large bank of ES cell lines [ 2 ].
In conjunction with research on stem cell biology and the development of potential stem cell therapies, research on approaches that prevent immune rejection of stem cells and stem cell-derived tissues should be actively pursued. These scientific efforts include the use of a number of techniques to manipulate the genetic makeup of stem cells, including somatic cell nuclear transfer.
Our panel includes members who participated in the workshop on stem cells held at the National Academies on June 23, This work shop was convened as part of the data-gathering process for the separate committee that produced the above report focused on stem cells. In our own workshop, held on August 7,we consulted with many of the world's leaders in nuclear transplantation to produce stem cells—I.
Trounson see Appendix C —and we have also conducted our own extensive literature review. On the basis of this review and discussion, the panel determined that although there is a clear therapeutic potential for techniques in which stem cells are produced through nuclear transplantation as in Figure 2this potential is nascent and needs considerable research.
The potential of this research includes developing a broader understanding of how human tissue cells develop normally and how human diseases that have a genetic component are caused at a cellular level. The panel concludes this executive summary with a review of the scientific subjects that were covered.
Five mammalian species have been reproductively-cloned from adult or fetal cells— sheep, mice, pigs, goats, and cattle—and similar attempts are being made, so far without success, in monkeys, dogs, and horses. The panel reviewed the scientific literature on animal cloning and heard from animal-cloning experts at its workshop.
It found that cloning efficiencies in animals remain extremely low despite several years of experimentation. This low efficiency means that any human reproductive cloning attempt would probably require large numbers of eggs.3 The resulting embryo, in a sense, is not a “true” clone, in that mitochondrial, or cytoplasmic, DNA from the Biological uncertainties about reproductive cloning, LANCET ; not participate in human cloning at this time because of the risk of physical harms, as well as psychosocial harms.
|Human cloning - Wikipedia||Updated Thursday 3rd August What happens during cloning?|
|The Pros and Cons of Cloning: Is it Worth the Risk?||For example, rather than purchasing a name-brand computer, we might purchase its clone, which provides close to the same benefits but at a lower cost. When biologists use the word clone, they are talking specifically about DNA molecules, cells, or whole plants or animals that have the same genetic makeup.|
|Executive Summary||Natural cloning[ edit ] Cloning is a natural form of reproduction that has allowed life forms to spread for hundreds of millions of years.|
- Human Cloning Human Cloning comes with two dangerous processes, reproductive cloning (the creating of a new organism) and the therapeutic cloning (the creation of a new tissues or “other biological products”) which affects the ethics of human society.
Until recently, discussions about human cloning were conducted within the realm of science fiction and fantasy. However, with the successful cloning of the sheep "Dolly" in , it became evident that sooner or later, scientists might be able to clone human beings, too.
Psychological and Ideological Aspects of Human Cloning: A Transition to a Transhumanist Psychology Introduction Science and technology are advancing so fast that society has difficulties in keeping pace with the human reproductive cloning (“Biological uncertainties”, ).
Problems related to the concept of uniqueness. The Ethical Implications of Human Cloning Department of Government,Harvard University, Cambridge Street,Cambridge,MA, E-mail:[email protected] This essay is based on a public lecture delivered at an international conference on cloning organized.
Scientific and Medical Aspects of Human Reproductive Cloning considers the scientific and medical sides of this issue, plus ethical issues that pertain to human-subjects research. Based on experience with reproductive cloning in animals, the report concludes that human reproductive cloning would be dangerous for the woman, fetus, and newborn, and is likely to fail.