Genetic Engineering: Cloning Essay, Research Paper
Genetic Engineering: Cloning
Genetic Engineering is defined as the scientific alteration of the structure of genetic material in a living organism, which involves the production and use of recombinant DNA .
A clone is a group of genetically identical cells. For example, tumors are clones of cells inside an organism because they consist of many replicas of one mutated cell. Another type of clone occurs inside a cell. Such a clone is made up of groups of identical structures that contain genetic material, such as mitochondria and chloroplasts. Some of these structures, called plasmids, are found in some bacteria and yeasts. Techniques of genetic engineering enable scientists to combine an animal or plant gene with a bacterial or yeast plasmid. By cloning such a plasmid, geneticists can produce many identical copies of the gene .
The term clone also refers to a group of organisms that are genetically identical. Most such clones result from asexual reproduction, a process in which a new organism develops from only one parent. Except for rare spontaneous mutations, asexually reproduced organisms have the same genetic composition as their parent. Thus, all the offspring of a single parent form a clone .
Strictly speaking a clone refers to one or more offspring derived from a single ancestor, whose genetic composition is identical to that of the ancestor. No sex is involved in the production of clones, and since sex is the normal means by which new genetic material is introduced during procreation, clones have no choice but to have the same genes as their single parent. In the same way, a clone of cells refers simply to the descendants of a single parental cell .
Scientists have long been intrigued by the possibility of artificially cloning animals. In fact, people have known since ancient times that some invertebrates (animals without backbones), such as earthworms and starfish, can be cloned simply by dividing them into two pieces. Each piece re-grows into a complete organism. The cloning of vertebrates, however, was much more difficult. The first leap forward in the cloning of these more complex organisms came in the 1950’s with work done on frogs .
Beginning in 1952, Robert Briggs and Thomas King, developmental biologists at the Institute for Cancer Research (now the Fox Chase Cancer Center) in Philadelphia, developed a cloning method called nuclear transplantation, or nuclear transfer, which was first proposed in 1938 by the German scientist Hans Spemann. In this method, the nucleus–the cellular structure that contains most of the genetic material and that controls growth and development–is removed from an egg cell of an organism, a procedure known as enucleation. The nucleus from a body cell of another organism of the same species is then placed into the enucleated egg cell. Nurtured by the nutrients in the remaining part of the egg cell, an embryo (an organism prior to birth) begins growing. Because the embryo’s genes came from the body cell’s nucleus, the embryo is genetically identical to the organism from which the body cell was obtained .
In their experiments, Briggs and King used body cells from frog embryos. From these cells, they were able to produce several tadpoles. The men used embryos consisting of only a few thousand cells as the source for body cells and nuclei, because at that stage of development an embryo’s cells are still relatively unspecialized. As an embryo develops into a completely formed organism consisting of billions of cells, its cells become increasingly specialized. Some cells become skin cells, for example, while others become blood cells. Skin cells can normally make only more skin cells. Likewise, blood cells can normally make only blood cells. By contrast, each of the unspecialized cells of an early embryo is capable of producing an entire body. At the time of Briggs’s and King’s experiment, researchers were not sure whether specialization occurs because different cells get different assortments of genes or because genes that are not needed in a particular kind of cell become inactive .
Additional research on nuclear transplantation was conducted in the 1960’s and 1970’s by John Gurdon, a molecular biologist at Oxford University in England. In 1966, Gurdon produced adult frogs using nuclei from tadpole intestine cells. This experiment proved that even cells that have undergone a great amount of specialization remain totipotent–capable, under certain circumstances, of directing the development of a complete organism. Totipotency implied that all of a fully developed organism’s body cells contain a complete set of genes and that specialization occurs because certain genes are active in some cells and inactive in other cells .
Despite the demonstrated totipotency of body cells, scientists were repeatedly frustrated in their attempts to use nuclear transplantation with nuclei taken from the cells of adult vertebrates. In the rare cases in which offspring resulted from such experiments, the young never survived to adulthood .
A different and simpler cloning procedure, called embryo splitting, or artificial twinning, was developed in the 1980’s and was adopted by livestock breeders. In this procedure, an early embryo is simply split into individual cells or groups of cells, as happens naturally with twins, triplets, and other multiple births. Each cell or collection of cells develops into a new embryo, which is then placed into the womb of a host mother animal, which carries it to a full term. Although this technique permits the production of multiple clones, the clones are derived from an embryo whose physical characteristics are not completely known rather than from an adult animal with known characteristics–a serious limitation for practical applications of the procedure. By the early 1990’s, embryo splitting and nuclear transplantation using cells from embryos had been used to clone a number of animals, including mice, cows, pigs, rabbits, and sheep .
Researchers said the cloning of animals, especially those that have been genetically modified in certain ways, could have a number of medical, agricultural, and industrial applications. For example, cloning could result in the mass production of genetically modified cattle that secrete valuable drugs into their milk. But the cloning of animals indicated that it might also be possible to clone humans. Much of the public expressed revulsion toward the prospect of human cloning, and some politicians vowed to outlaw it. Its proponents, however, saw human cloning as a way to help people, such as by allowing infertile couples to have children .
Transgenic animals (animals engineered to carry genes from species other than their own) can be made to produce a wide variety of proteins that could be sold as drugs, as well as other proteins, called enzymes, that could be used to speed up industrial chemical reactions. Although the creation of transgenic animals began in the 1980’s, cloning was expected to make it possible for such animals to be mass-produced. Large numbers of transgenic animals could produce vast quantities of needed drugs and other useful substances more efficiently and at much lower cost than is possible with bioengineering methods. As of mid-1998, most genetically engineered proteins were being manufactured in bioreactors, large steel vessels in which billions of genetically modified microorganisms produce proteins that are then extracted and purified .
Researchers involved in cloning envision a number of other practical applications for their work, including the creation of genetically modified animals that could provide organs for human organ transplants; the mass production of faster-growing and leaner livestock; and the perpetuation of endangered species .
The same procedures used to clone sheep and cattle could theoretically be used to clone humans. However, human cloning would probably be more difficult than sheep or cattle cloning, because the cells of human embryos start producing proteins at a relatively early stage. Thus, there would not be as much time for the egg cytoplasm to reprogram a transplanted nucleus. However, the successful 1998 cloning of mice, which also start producing proteins at
Geneticists foresee a number of practical applications for the cloning of humans. Infertile couples that do not wish to adopt, for instance, could use cloning to have children who are biologically related to them. Cloning could also be used to produce offspring free of certain diseases. For example, a number of disorders, including some affecting the eyes, brain, and muscles, are (at least partially) caused by flawed genes located in the mitochondria, energy-producing structures in the cytoplasm. If a woman were to carry a gene for one of these disorders, she could conceive a healthy child by having the nucleus of one of her body cells inserted into an enucleated egg cell from a woman who does not have anything wrong with her mitochondrial genes. The resulting embryo could then be implanted into the woman who donated the nucleus, and she would carry the baby to term .
Some proposed practical applications of cloning: the mass production of animals engineered to carry human genes for the production of certain proteins that could be used as drugs; the proteins would be extracted from the animals’ milk and used to treat human diseases, the mass production of animals with genetically modified organs that could be safely transplanted into humans, the mass production of livestock that have been genetically modified to possess certain desirable traits (ex. Scientists at Texas A&M University in College Station unveiled a disease-resistant black Angus bull, saying it could lead to safer beef and more efficient ranching worldwide), the perpetuation of endangered species, the production of offspring by infertile couples, and the production of offspring free of a potentially disease-causing genetic flaw carried by one member of a couple; the individual without the defect could be cloned .
Some people may think that biologists are cloning human embryos only to see how far they can push the scientific envelope, but there are many legitimate reasons for investigating cloning. Embryologists believe that research into cloning could help improve the life of future generations. Many biologists believe that they have a personal duty to the improvement of society, perhaps even a moral obligation. To this end the techniques of embryonic cloning and alteration have been offered to society as an option for the improvement of humanity. Doctors hope that by being able to study the multiple embryos developed through cloning, they can determine the causes of spontaneous abortions. Contraceptive specialists believe that if they can determine how an embryo knows where to implant itself, they can develop a contraceptive that would prevent embryos from implanting in the uterus. Cancer research is possibly the most important reason for embryo cloning. Oncologists believe that embryonic study will advance understanding of the rapid cell growth of cancer. Cancer cells develop at approximately the same phenomenal speed as embryonic cells do. By studying the embryonic cell growth, scientists may be able to determine how to stop it, and also stop cancer growth in turn .
Another important area of embryo cloning research is embryonic stem cell development. Stem cells are undifferentiated cells that can develop into almost any type of cell in the body. These cells are not attacked by a person s immune system, because of their fast development and undifferentiated status. Many doctors believe that these stem cells could be used in treatments for brain and nervous system damage. In adult humans, when damage to nerve tissue takes place, the nerve tissue does not regenerate and replace the lost tissue. However, since the stem cells are undifferentiated they could theoretically be used to replace the damaged cells. Human embryo cloning is needed for the implantation of stem cells, because of the large amount of cells that would be needed. Genetic screening is a branch of cloning research that is already being used in hospitals in England. Parents who have a history of genetically inherited disease, such as cystic fibrosis, can use embryo screening to determine if their child has received the defective gene. Several embryos can be developed via in vitro fertilization procedures, and then be cloned. The DNA from one of the cloned embryos would then be removed and standard genetic testing, using riflips, would be used to detect whether or not that embryo contained the genetic disease. If the cloned embryo does not contain the defective gene, then one of the other identical embryos can be used for implantation in the parent. This would almost guarantee that the child would be free of the genetic disease .
Perhaps a more questionable use of cloned embryos is for spare parts. It is possible that parents could decide to use one cloned embryo for implantation and eventual birth of a child, and save any spares by freezing them. If the child were to become critically sick, and need a bone marrow transplant, one of the frozen embryos could be thawed and implanted into the uterine wall for development of another identical child. The bone marrow from this child could then be used to help save the life of the child, perhaps even without the necessity of carrying the child to full term. This again raises the question of what moral status a fetus should have, if any at all .
Because human embryo research is just in its infancy, there has been a rush to decide what guidelines are going to be instituted for governing cloning experiments. To assist the National Institutes of Health (NIH) in determining which cloning experiments to fund, a medical panel was set up to form a preliminary set of guidelines. Steven Muller, the head of the panel, set out with the help of several prominent biologists including, Brigid Hogan and embryology specialist Mark Hughes, to put together a set of guidelines that would satisfy the concerns of both the scientific and religious communities. The religious community vigorously opposes all human cloning procedures. The scientific community sympathizes with the religious communities concerns, but does not want to lose the enormous amount of information that may be gained by human embryo cloning. Muller’s panel announced a set of guidelines that they hope would be acceptable to both communities. They recommended research be permitted on preexisting embryos. These embryos would be allowed to develop up to and including the fourteenth day. Researchers would also be allowed to produce new embryos only for what the NIH considers “compelling research.” Researchers would also be permitted to remove some of the embryonic cells from embryos that are destined for in vitro fertilization at a later time .
The panel did not come to a decision in several other areas of research funding. Research on fetal oocytes and research on embryos whose donator is unavailable to give consent were left undecided. The panel suggested that research might be permitted after the fourteenth day of development depending on the circumstances, but definitely not after the eighteenth day, when neural tube closure begins. The neural tube is the beginning of the nervous system, including the brain, in adult humans. The experiments that the panel recommended be banned include impregnating human embryos in other animal species, impregnating cloned embryos into humans, the use of embryos for sex selection, or the transfer of one nucleus from one embryo to another .
These are but a few of the procedures that the panel felt were inappropriate for federal funding. The above limitations only apply to federally funded experiments. Currently there are no laws directly prohibiting any of the above procedures in private research settings (Clinton has stopped funding for federal experiments). It should also be stated that all of the above procedures have or can be carried out with current technology .
In conclusion, cloning humans would have many major benefits, yet like all great things, there are side effects. The moral issues sometimes outweigh the obvious facts. The only thing left to do is wait and see if human cloning will arise in the next few years. It is a definite observation that there will be attempts; however, may they be successful or not, the cloning of humans could lead to a world of immortality.