Cloned animals have hundreds of abnormal genes, which explains why so many of them die at or before birth, meaning it would be irresponsible to clone a human being. Despite this, there are several human cloning attempts taking place right now.
The process of cloning introduces the genetic mutations, and this seems to be unavoidable. Rudolf Jaenisch of M.I.T. says, "I think this confirms suspicions that I have always had and that many others had that cloning is a very inefficient method at this point. It is very irresponsible to think this method could be used for the reproductive cloning of humans."
The most common cloning method is nuclear transfer, which involves taking the nucleus out of an egg cell, replacing it with the nucleus from a cell of the animal to be cloned, and then "reprogramming" it so the egg begins dividing as if it had been fertilized by a sperm.Only one of every several hundred eggs ever starts dividing and only a small percentage of these result in pregnancies. And many of the animals that survive die soon after birth, or develop abnormalities of the lung, liver and other organs.
Jaenisch and his colleagues made dozens of cloned mice and then looked at their genes and found many abnormalities. The difference was so clear that they could tell normal mice from cloned mice by looking at their genes. "There is no reason in the world to assume that any other mammal, including humans, would be different from mice," Jaenisch says. "It settles the old question?about how normal can clones be."
Several cloning researchers say their cloned livestock, such as cattle, sheep and pigs, are normal and healthy, if they get past birth. But Jaenisch believes genetic abnormalities will be found even in these seemingly normal animals. Some of them aren?t obvious because they?re not fatal.
Many of the problems were in imprinted genes, which are involved in the development of the embryo. In the imprinting process, only the copies of a gene that a baby gets from its father are turned on. "Almost 50 percent of those were incorrectly expressed," Jaenisch says. That means that cloning technology to make human cells for use in medical treatments will probably be safe. "In therapeutic cloning you don't form an embryo," Jaenisch says. "In cloning most, if not all, problems arise during embryonic development."
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