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. Turns out, ethics aren't the only thing holding scientists back.
Cloning isn't the sci-fi marvel we think it is. It can be dangerous, often ineffective, and, most of all, we just haven't thought of a good enough reason to do it. So, here's why you'll probably never have to fight your evil clone.
This is Dolly. Just kidding, that's a regular sheep. This is Dolly, the first mammal cloned successfully from an adult cell. She was born in after scientists figured out how to remove the DNA from the egg cell of a Scottish Blackface sheep and basically replace it with the DNA of a mammary cell from a Finn Dorset sheep. They gave it a little electric shock to fuse the cell and get it replicating, placed the cells in the uterus of another sheep, and boom, clone.
This method, called reproductive cloning, could theoretically be used on humans. But this is a best-case scenario. It took tries for the scientists to get one Dolly. Better than one in , but still a majorly inefficient process. Jose Cibelli: Technically, it's not difficult to produce a clone embryo, but human cloning has other hurdles that need to be considered. Narrator: To even research human cloning, scientists would need to ethically collect a large amount of donated eggs and find enough surrogates to carry them.
But even if they made it through that logistical nightmare, the biggest issue is this:. Some embryos expire in the IVF dish. Others wither in the womb. Of those that are born, a few suffer from abnormalities and quickly die. Nevertheless, cloning moved forward in cattle and pet dogs.
Failed clones are just a cost of doing business. The cause of the problems is better understood today. So many are simply shut off. The reason cloning works at all is that an egg has a remarkable ability to turn genes back on through a process called reprogramming.
Yet the egg has only hours to do the job, and some genes are resistant. He said Zhang has found chemicals that, if added to an egg, can help release the blocked genes. Zhang first tried it with mice. Zhang then tried the process on human eggs. In , his team recruited four women to have eggs drawn from their ovaries.
Into these, they injected skin cells from other people. Without the gene-releasing molecules, the cloned embryos never developed correctly. With the modifiers, though, about a quarter of them did. Instead, his objective in cloning speck-size human embryos is to obtain their stem cells. Follow Rachael Rettner RachaelRettner.
Originally published on LiveScience. Rachael has been with Live Science since She also holds a B. Live Science. Rachael Rettner.
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