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Genetic Cloning

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A controversial issue of the twenty-first century is the possible application of new techniques in genetic engineering to produce human clones. Up until now genetic engineering and cloning has been used to clone plants, unicellular organisms, amphibians and simple mammals. This has led to significant advances in agriculture, industry, and medicine. Newer techniques in genetic engineering have enabled scientists to clone more complex mammals and opened up the possibility of cloning humans. Although there are many potential benefits to this technology, the prospect of cloning humans has raised many practical, ethical and religious dilemmas that are currently being debated by society. As of now, the actual cloning of humans does not seem likely to occur in the foreseeable future.

Genetic engineering is the changing of an organism's DNA, genetic material to eliminate unwanted traits or to produce desirable traits. The earliest form of genetic engineering dates back to the scientist Gregor Mendel who did experiments with peas. He bred only the peas with the most desirable traits in order to achieve a healthier and stronger pea (McCuen 8). This method, called selective breeding, is still used today with plants and animals in order to increase food production. Corn plants are selectively bred in order to produce a larger tastier kernel. Another type of genetic engineering called hybridization or crossbreeding involves breeding animals of different species in order to obtain the most desirable traits of both. Male donkeys are crossbred with female horses to produce mules, which are good work animals (Levine 1).

In 1938, Hans Speman proposed cloning a mammal by transplanting an adult cell's nucleus into a fertilized egg. This process is called nuclear transfer and was initially used to clone a frog in 1952 (Sinha 59). Using this process, nuclear DNA from the body cell of a donor frog was injected into the egg cell of a recipient frog whose nuclear genetic material was removed. The fused cells divided just like a normal fertilized egg and formed an embryo that was genetically identical to the donor frog. In 1980 mice were successfully cloned using a similar procedure. The nucleus of a body cell of an embryo removed from a pregnant mouse was placed into a fertilized egg of another mouse whose own nucleus was removed. The cell was grown in vitro until it divided and became an embryo. It was then implanted into another mouse and allowed to grow to term. Mammalian clones of sheep were reproduced in this fashion as well in 1984. This type of cloning needed to use embryonic cells. Almost all of an animal's cells contain the genetic material needed to reproduce that animal. However, as cells differentiate into different tissues and organs, they only keep the genetic material needed to reproduce that organ. Therefore, only embryonic cells can be used for cloning because they have not differentiated into a specific type of tissue and still retain all the genes needed to make a copy of themselves (From Year in Review 1997 1). Although this method of cloning has been successful, most nuclear transfers do not result in live offspring. In addition, there have been a lot of objections raised regarding the use of embryos to clone mammals. Many people object based on religious grounds that the embryo has a soul from the moment of conception and therefore it should not be tampered with. Scientists were hoping that they could clone mammals without the use of embryos (Beddington 3).

In 1996, Ian Wilmut, at the Roslin Institute, accomplished this feat. He was able to successfully clone a sheep without the use of embryonic cells. Dolly the sheep was successfully cloned by transferring the nucleus of a non-reproductive cell, a mammary cell, into an unfertilized sheep egg from which its own genetic material had been removed. Dolly was an exact clone of the sheep that donated the mammary cell. Using a mammary cell was unique since until now only embryonic cells could develop into a full organism. Ian Wilmut was able to reprogram an adult cell to dedifferentiate and therefore the cell retained the genetic material needed to produce an entire organism and not just a mammary cell. The key to this new procedure was to time the cell cycle of the mammary cell with that of the egg. In order to do this nutrients were withheld from the mammary cell, which stopped it from dividing. The nucleus of the mammary cell was transferred into the recipient egg. An electrical current was given to the egg, which provided the energy that was needed for fertilization to occur. The egg began to divide and when it became an embryo it was placed into another sheep. The lamb that was born, Dolly was a clone of the donor of the original mammary cell (Kolata 27). This type of cloning is very exciting. This technique may be used to mass-produce animals that mimic human diseases for research purposes or to create animals with genetically modified organs that could be safely transplanted into humans. It could also be used to mass-produce animals for drug production or to improve livestock (Clone 1).

This new technique can theoretically also be used to clone humans. However, there are technical difficulties in cloning using a human egg. The unfertilized egg of a mammal has a supply of proteins that is used by the embryo until the embryos own genes can make the proteins for itself. Sheep embryos rely on their own genes after four cell divisions which is apparently enough time for the foreign nucleus to take over and reprogram the egg. However, human embryos begin producing proteins at an earlier stage so there is not a lot of time for the egg cytoplasm to reprogram the nucleus that was transplanted. This makes it harder to clone humans than it is to clone sheep. However, mice also begin producing proteins at an early stage and they were successfully cloned in 1998. This shows us that human cloning is theoretically possible even though they produce proteins at an early stage (Beddington 4).

There is currently a great debate going on concerning human cloning and the continuation of cloning research in general. People in favor of human cloning argue that human cloning would be useful in many ways. It would make it possible for infertile couples to have children of their own who are biologically related to them. Instead of having to use donated embryos, the couple could use their own adult cells to fertilize the egg. In addition, if a woman only has one egg, cloning could be used to make many copies of that egg. This would significantly increase her chances of getting pregnant. It would also enable couples who were at risk of having children with a genetic defect able to have perfectly healthy and normal children. For example, defective genes located in the mitochondria of the cell cause some diseases. If a woman carries a defective gene in her mitochondria she could still produce



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