Therapeutic cloning works in a similar way to reproductive cloning. A cell is taken from an animal's skin and is inserted into the outer membrane of a donor egg cell. Then, the egg is chemically induced so that it creates embryonic stem cells. These stem cells can be harvested and used in experiments aimed at understanding diseases and developing new treatments. The first study of cloning took place in , when German scientist Hans Adolf Eduard Driesch began researching reproduction.
In , he was able to create a set of twin salamanders by dividing an embryo into two separate, viable embryos, according to the Genetic Science Learning Center. Since then, there have been many breakthroughs in cloning.
In , British biologist John Gurdon cloned frogs from the skin cells of adult frogs. On July 5, , a female sheep gave birth to the now-famous Dolly, a Finn Dorset lamb — the first mammal to be cloned from the cells of an adult animal — at the Roslin Institute in Scotland. Since Dolly, many more animal clones have been born , and the process is becoming more mainstream.
Research has also been conducted on human-cell cloning. In , scientists at Oregon Health and Science University took donor DNA from an 8-month-old with a rare genetic disease and successfully cloned human embryonic stem cells for the first time.
Unfortunately, the researchers didn't remove the cells to save the child. The project was to prove that mature donor cells could be used to produce new ones. This research has evolved into using stem cells for many different applications, including hair regrowth, treatments for burns and more. Several companies are currently providing services that use cloning technology. Even plants are being cloned. One company is cloning maple trees to provide lumber for guitar-makers, with the aim of duplicating a quality in the wood, called figuring, that gives a guitar a sort of shimmering appearance.
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? How are genes cloned? How are animals cloned? What animals have been cloned?
Have humans been cloned? Do cloned animals always look identical? What are the potential applications of cloned animals? What are the potential drawbacks of cloning animals? What is therapeutic cloning?
What are the potential applications of therapeutic cloning? What are the potential drawbacks of therapeutic cloning? This experiment showed that each cell in the early embryo has its own complete set of genetic instructions and can grow into a full organism. Spemann fashioned a tiny noose from a strand of baby hair and tightened it between two cells of a salamander embryo until they separated. Each cell grew into an adult salamander.
Again using a strand of baby hair tied into a noose, Spemann temporarily squeezed a fertilized salamander egg to push the nucleus to one side of the cytoplasm. The egg divided into cells—but only on the side with the nucleus.
After four cell divisions, which made 16 cells, Spemann loosened the noose, letting the nucleus from one of the cells slide back into the non-dividing side of the egg. The single cell grew into a new salamander embryo, as did the remaining cells that were separated.
Essentially the first instance of nuclear transfer, this experiment showed that the nucleus from an early embryonic cell directs the complete growth of a salamander, effectively substituting for the nucleus in a fertilized egg.
Briggs and King transferred the nucleus from an early tadpole embryo into an enucleated frog egg a frog egg from which the nucleus had been removed. The resulting cell developed into a tadpole. The scientists created many normal tadpole clones using nuclei from early embryos.
Most importantly, this experiment showed that nuclear transfer was a viable cloning technique. It also reinforced two earlier observations. Second, embryonic cells early in development are better for cloning than cells at later stages.
Gurdon transplanted the nucleus of a tadpole intestinal cell into an enucleated frog egg. In this way, he created tadpoles that were genetically identical to the one from which the intestinal cell was taken. This experiment showed that, despite previous failures, nuclei from somatic cells in a fully developed animal could be used for cloning. Importantly, it suggested that cells retain all of their genetic material even as they divide and differentiate although some wondered if the donor DNA came from a stem cell, which can differentiate into multiple types of cells.
Mammalian egg cells are much smaller than those of frogs or salamanders, so they are harder to manipulate. Using a glass pipette as a tiny straw, Bromhall transferred the nucleus from a rabbit embryo cell into an enucleated rabbit egg cell. He considered the procedure a success when a morula, or advanced embryo, developed after a couple of days. This experiment showed that mammalian embryos could be created by nuclear transfer.
To show that the embryos could continue developing, Bromhall would have had to place them into a mother rabbit's womb. He never did this experiment. Willadsen used a chemical process to separated one cell from an 8-cell lamb embryo. The he used a small electrical shock to fuse it to an enucleated egg cell. As luck would have it, the new cell started dividing. By this time, in vitro fertilization techniques had been developed, and they had been used successfully to help couples have babies.
So after a few days, Willadsen placed the lamb embryos into the womb of surrogate mother sheep. The result was the birth of three live lambs. This experiment showed that it was possible to clone a mammal by nuclear transfer—and that the clone could fully develop. Even though the donor nuclei came from early embryonic cells, the experiment was considered a great success. Using methods very similar to those used by Willadsen on sheep, First, Prather, and Eyestone produced two cloned calves.
Their names were Fusion and Copy. This experiment added cows to the list of mammals that could be cloned by nuclear transfer.
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