But Ian Wilmut, who created Dolly the sheep, says Advanced Cell's work on cows is encouraging.
Such nuclear transfer produced Dolly the sheep, the world's first cloned mammal, four years ago.
An ethical debate on cloning has been brewing ever since Dolly the sheep was produced in 1997.
Also Wednesday, the researchers who cloned Dolly the sheep introduced five cloned pigs in the journal Nature.
Even Dolly the sheep, who was produced by cloning via somatic nuclear cell transfer, benefited from a male imprinted genome.
The centre became famous in 1996 for creating Dolly the sheep - the first mammal to be cloned from an adult cell.
Instead, they want to use somatic cell nuclear transfer, the same process used to clone Dolly the sheep in 1997, to create embryonic stem cells.
Thirteen years ago, the world's first mammal to be cloned using DNA from an adult cell, Dolly the Sheep, was born in Edinburgh.
Dolly the sheep was the world's first mammal cloned from the DNA of an adult cell and was unveiled to the public in 1997.
In 1997, when Dolly the sheep became the first mammal to be cloned from an adult sheep, cloning a human entered the realm of possibility.
However, the technique is so close to the "cloning" technology used to create Dolly the sheep that it will raise difficult ethical questions for doctors.
Right now, scientists can only use stem cells to study particular diseases by creating embryos through the same process used to clone animals like Dolly the sheep.
From this year on, starting with Dolly the sheep, we do have proof there is a third subject which is able to develop species - that is human beings.
His role in cloning Dolly the sheep, the world's first clone from an adult cell, led to an OBE in 1999 and he has been elected to five scientific academies worldwide.
The prospect of cloning a human moved from science fiction into the realm of possibility in 1997, when Dolly the sheep became the first mammal to be cloned from an adult.
Dolly the sheep -- the first cloned animal -- was created over 10 years ago, and the only previous claim of human embryo cloning by South Korean scientist Woo Suk Hwang in 2004, was discredited.
Reproductive cloning, which created Dolly the sheep in 1997, involves transferring the nucleus of an adult cell into an egg, giving the resulting embryo a full set of genes without the normal sperm-meets-egg fertilisation step.
It is a technique called nuclear transfer -- the same used to create Dolly the sheep -- and until Mitalipov's research there had been skepticism over whether a primate could be cloned in the same manner.
His role at the Roslin Institute in cloning Dolly the sheep, the world's first clone from an adult cell, led to an OBE in 1999 and he has been elected a fellow of five scientific academies worldwide.
Dr. Alan Colman, a member of the team that cloned Dolly the sheep -- the first cloned mammal -- in 1997, told CNN that within 20 years stem cell therapies could be used to treat degenerative diseases such as diabetes, congestive heart failure and Parkinson's disease.
When his daughter Mary's novel "Frankenstein, or the Modern Prometheus" was published in 1818, its readers were well primed to recognize the dreams and nightmares it reflected rather, perhaps, as we today might be expected to catch a reference to Dolly the cloned sheep.
The new study involves something similar to the cloning technique that led to the birth of Dolly, the famous cloned sheep that was born in July 1996.
Dolly and the donor sheep were genetically identical, like twins, except that the clone was much younger than the other.
In the more than three years since scientists in Britain cloned the sheep Dolly, other researchers have successfully cloned sheep, cows, goats, pigs and mice.
On June 21, the United Kingdom granted two patents for technologies that were used in creating the cloned sheep Dolly in 1997.
Dr Ian Wilmut, who created Dolly, the world's first cloned sheep, said it took 277 tries to get it right.
They produced a lively and, to all intents and purposes, normal sheep, known as Dolly, from the nucleus of a mammary-gland cell.
The Roslin Institute's Dr. Ian Wilmut, who pioneered the technique that cloned Dolly from a single mammary cell from an adult sheep, said that while human cloning is theoretically possible, he saw no reason to do so.
We will never know in the case of Dolly whether her condition is due to cloning or whether it is an unfortunate accident because sheep do develop arthritis.
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