The same kind of decrease in LOS rates was observed as people who used technologies such as in vitro fertilization in cattle learned more about the process. Most clones that are normal at birth become as strong and healthy as any other young animals.
Calf and lamb clones with abnormalities at birth may continue to have health problems for the first few months of life. Lots of people get this confused. They just do the same thing as their conventionally bred counterparts. Cows that make pharmaceuticals in their milk are genetically engineered—that is, they have new genes added to them. Some of these genetically engineered animals can be reproduced by cloning, which is why some people get confused about this concept.
Neither chickens nor any other kind of bird have been cloned yet. So far, mice, rats, rabbits, cattle and the closely related but endangered gaurs and bantengs , swine, sheep, goats, deer, horses, mules, cats, and dogs are the mammals that have been cloned. After years of detailed study and analysis, FDA has concluded that meat and milk from clones of cattle, swine, and goats, and the offspring of clones from any species traditionally consumed as food, are as safe to eat as food from conventionally bred animals.
In addition, cloning may also be a way to duplicate a disease-resistant animal, and over generations create a disease-resistant herd. Well, okay, but how about cloning endangered species? Scientists have cloned sheep from very small populations, members of rare cattle breeds, and the gaur and banteng, two species closely related to domesticated cattle species.
Back to the top Myth: Offspring of clones are clones, and each generation gets weaker and weaker and has more and more problems. Back to the top Myth: Clones are always identical in looks. Not necessarily. The result is CC's black and white tiger-tabby coat. Rainbow and CC are living proof that a clone will not look exactly like the donor of its genetic material.
Programs are underway to clone agricultural animals, such as cattle and pigs, that are efficient producers of high-quality milk or meat. A group of researchers at Utah State University led by Dr. Their aim isn't to produce animals for consumption—cloning is far more labor-intensive and expensive than conventional breeding methods. Instead, they want to use these animals as breeding stock. The important thing to know about beef cattle is that the quality and yield of their meat can be assessed only after they are slaughtered.
And male animals are routinely neutered when they're a few days old. That is, their testes are removed, so they are unable to make sperm. But cells from a high-quality carcass can be cloned, giving rise to an animal that is able, though conventional breeding methods, to pass its superior genes to its offspring. Scientists have also cloned mules, a reproductively sterile hybrid of a male donkey and a female horse; dairy cows; and horses.
One gelded racing horse, a male whose testes have been removed, has a clone that is available for breeding. Some of the cloned cows produce about twice as much milk as the average producer. And a cloned racing mule is ranked among the best in the world. Farm animals such as cows, sheep, and goats are being genetically engineered to produce drugs or proteins that are useful in medicine.
As an example, scientists could take cells from a cow that produces large amounts of milk and grow them in culture. Then they could insert a gene into the DNA of these cells that codes for a drug or a vaccine. If they take the nucleus from one of these cells and transfer it to a cow egg, it could develop into a cow that makes the drug in its milk. Since every cell in the cow would carry the drug gene, it could pass the gene to its offspring, creating a whole herd of drug-producing cows.
Even better, we could avoid the issue of the genetic reshuffling that happensduring sexual reproduction and simply clone our drug-producing cow. The prospect of cloning humans is highly controversial, and it raises a number of ethical, legal, and social challenges that need to be considered. The vast majority of scientists and lawmakers view human reproductive cloning—cloning for the purpose of making a human baby—immoral.
Supporters see it as a possible solution to infertility problems. Some even imagine making clones of geniuses, whose work could advance society.
Far-fetched views describe farms filled with clones whose organs are harvested for transplantation—a truly horrific idea. For now, risks and technical challenges—as well as laws that make it illegal—will probably keep human reproductive cloning from becoming a reality. Even though many species have been cloned successfully, the process is still technically difficult and inefficient.
The success rate in cloning is quite low: most embryos fail to develop, and many pregnancies end in miscarriage. Current efforts at human cloning are focused on creating embryonic stem cells for research and medicine, as described above. Support us Find out more. Receive our newsletter. This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish.
Accept Read More. Cookies Policy. Close Privacy Overview This website uses cookies to improve your experience while you navigate through the website. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website.
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.
0コメント