There are three different types of artificial cloning: gene cloning, reproductive cloning and therapeutic cloning. Gene cloning produces copies of genes or segments of DNA. Reproductive cloning produces copies of whole animals. Therapeutic cloning produces embryonic stem cells for experiments aimed at creating tissues to replace injured or diseased tissues. Gene cloning, also known as DNA cloning, is a very different process from reproductive and therapeutic cloning.
Reproductive and therapeutic cloning share many of the same techniques, but are done for different purposes. Researchers routinely use cloning techniques to make copies of genes that they wish to study. The procedure consists of inserting a gene from one organism, often referred to as "foreign DNA," into the genetic material of a carrier called a vector. Examples of vectors include bacteria, yeast cells, viruses or plasmids, which are small DNA circles carried by bacteria.
After the gene is inserted, the vector is placed in laboratory conditions that prompt it to multiply, resulting in the gene being copied many times over. In reproductive cloning, researchers remove a mature somatic cell , such as a skin cell, from an animal that they wish to copy.
They then transfer the DNA of the donor animal's somatic cell into an egg cell, or oocyte, that has had its own DNA-containing nucleus removed. Researchers can add the DNA from the somatic cell to the empty egg in two different ways. In the first method, they remove the DNA-containing nucleus of the somatic cell with a needle and inject it into the empty egg.
In the second approach, they use an electrical current to fuse the entire somatic cell with the empty egg. In both processes, the egg is allowed to develop into an early-stage embryo in the test-tube and then is implanted into the womb of an adult female animal. Ultimately, the adult female gives birth to an animal that has the same genetic make up as the animal that donated the somatic cell. This young animal is referred to as a clone.
Reproductive cloning may require the use of a surrogate mother to allow development of the cloned embryo, as was the case for the most famous cloned organism, Dolly the sheep. Over the last 50 years, scientists have conducted cloning experiments in a wide range of animals using a variety of techniques.
In , researchers produced the first genetically identical mice by splitting mouse embryos in the test tube and then implanting the resulting embryos into the wombs of adult female mice. Shortly after that, researchers produced the first genetically identical cows, sheep and chickens by transferring the nucleus of a cell taken from an early embryo into an egg that had been emptied of its nucleus.
It was not until , however, that researchers succeeded in cloning the first mammal from a mature somatic cell taken from an adult animal. After attempts, Scottish researchers finally produced Dolly, the lamb from the udder cell of a 6-year-old sheep. Two years later, researchers in Japan cloned eight calves from a single cow, but only four survived.
Besides cattle and sheep, other mammals that have been cloned from somatic cells include: cat, deer, dog, horse, mule, ox, rabbit and rat. In addition, a rhesus monkey has been cloned by embryo splitting. Despite several highly publicized claims, human cloning still appears to be fiction. There currently is no solid scientific evidence that anyone has cloned human embryos. In , scientists in South Korea claimed to have successfully cloned a human embryo, but said the experiment was interrupted very early when the clone was just a group of four cells.
In , Clonaid, part of a religious group that believes humans were created by extraterrestrials, held a news conference to announce the birth of what it claimed to be the first cloned human, a girl named Eve. However, despite repeated requests by the research community and the news media, Clonaid never provided any evidence to confirm the existence of this clone or the other 12 human clones it purportedly created.
In , a group led by Woo-Suk Hwang of Seoul National University in South Korea published a paper in the journal Science in which it claimed to have created a cloned human embryo in a test tube. However, an independent scientific committee later found no proof to support the claim and, in January , Science announced that Hwang's paper had been retracted.
From a technical perspective, cloning humans and other primates is more difficult than in other mammals. One reason is that two proteins essential to cell division, known as spindle proteins, are located very close to the chromosomes in primate eggs. Consequently, removal of the egg's nucleus to make room for the donor nucleus also removes the spindle proteins, interfering with cell division.
In other mammals, such as cats, rabbits and mice, the two spindle proteins are spread throughout the egg. So, removal of the egg's nucleus does not result in loss of spindle proteins. In addition, some dyes and the ultraviolet light used to remove the egg's nucleus can damage the primate cell and prevent it from growing.
US-based Tetra is the first in a series of cloned monkeys that scientists could use as test subjects to learn more about diseases like diabetes. Guar what now? A Guar is an Asian ox that has been dwindling in numbers. Thankfully, they were succesfully cloned in Sadly, Noah lived for two days and died of dysentery soon after.
Copy Cat could well be the starting gun for an entirely new industry of pet clones. Created in Copy Cat, was, well, a domestic cat. Copy Cat was the world's first cloned pet. Given the never-ending game of cat and, ahem, rat it is only fair to include Ralph. Ralph was one, or is it legion, of three rat pups created in Ralph's genetic makeup may well be used in research labs in the future. Ok, so not a legion of rats, but it sounded cool ok?
Is is just me who believes that rats aren't exactly in need of cloning technology? Mules are sterile right? Not if you clone them! Well yes, they are still sterile but this is a great way of sticking your middle finger up to biological boundaries. Idaho Gem was born in No, not Prometheus damn your devious mind unless, well actually yes if you can speak Greek, of course. An Italian team created this cloned horse in The belief was that they could "mass produce" Italian stallions. Sadly the experiment failed.
She was birthed by her own clone source "parent". Being endangered is not a prerequisite of cloning potential. The African Wildcat was cloned for no other reason than we just can. US scientists used Ditteaux as a template for cloning other, more vulnerable animals.
The kitten was born Dec. Though the kitten — nicknamed CC, short for Carbon Copy — was genetically identical to the cat Rainbow, the patterns on her fur looked different, likely due to developmental, rather than genetic, factors, the study said. CC had her own kittens a few years later. Dewey is still alive today. In , researchers in Italy cloned a female horse, which they named Prometea. Interestingly, the female that gave birth to Prometea was also the donor of the genetic material, according to the study.
The authors noted that the successful cloning of Prometea helped dispel notions that it might be unsafe for immune-related reasons for a mother to carry a fetus that was genetically identical to herself to term. Their results were published in Nature in Researchers in South Korea cloned a dog, according to their results published in Nature in The puppy, named Snuppy, was born April 24, He was cloned from adult skin cells taken from an Afghan hound, according to the study.
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