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- The brave new world will have to wait a little longer.
The cloning technology that produced Dolly the sheep will never be able
to produce identical humans, research has shown.
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- Four genetically identical sheep bred, like Dolly, at
the Roslin Institute in Edinburgh, have grown up with marked differences
in their appearance and behaviour - suggesting that any human who tried
to recreate themselves would be doomed to disappointment.
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- Professor Keith Campbell, who worked on the cloning programme
at the Roslin Institute and who helped to create the four ram clones, said
the animals had increasingly diverged from one another with age.
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- "They look similar, as sheep from the same breed
do, but you would not know they are clones," he said. They have developed
different sizes and temperaments.
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- Roslin, headed by Dr Ian Wilmut, made history in 1997
when it announced the creation of Dolly, the first mammal to have been
cloned from an adult cell. It led to predictions that humans could also
soon be cloned - allowing tycoons and dictators to perpetuate themselves
indefinitely.
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- The film Boys from Brazil, starring Gregory Peck, portrayed
such a possibility with Hitler clones created around the world by renegade
Nazi scientists. Some foresaw serious commercial applications such as the
cloning of top racehorses or pet dogs. But such ideas may lie in tatters
thanks to Cedric, Cecil, Cyril and Tuppence, four Dorset rams that were
created from genetically identical embryonic sheep cells.
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- If such cloning worked exactly they should, theoretically,
have been carbon copies of each other. In reality, a host of other factors
have conspired to make them into unique individuals. Campbell is unable
to say exactly why the animals differ: research into the causes has not
been done. High among the possibilities is the fact that the four-cell
nuclei from which they were created were placed into egg cells taken from
different female sheep. The contents or cytoplasm of those egg cells would
each have interacted with the introduced nuclei in slightly different ways.
In particular, the mitochondria, the parts of the cell that convert chemicals
into energy, contain separate DNA, amounting to about 3% of that found
in the nucleus.
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- It means that the mitochondrial DNA from each of the
different mothers may have interacted with the nuclei in ways that could
have been different enough to alter the growing embryo and hence the adult
sheep.
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- Dr Harry Griffin, assistant director for science at Roslin,
said the quality of the eggs would also have varied. "Just like in
women undergoing fertility treatment, the eggs of sheep can vary in quality
and that will help determine the viability of the embryo and possibly the
appearance of the adult," he said.
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- Other factors that could make clones appear different
from one another include mutation - where cells fail to replicate perfectly
as they divide. If this happened in an embryo it could affect all the subsequent
cells and so slightly alter the resulting adult.
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- Additionally, the genes that control the way an animal
grows or behaves are subject to a switching system so that they turn themselves
on and off at the appropriate times. In humans, these switches control
factors such as growth or the onset of puberty - but they are also subject
to environmental factors that could be different between clones.
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- The Roslin researchers say that overall their results
show that the resurrection of lost loved ones, human or animal, will never
be possible using the method that created Dolly.
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- Such assertions will disappoint cloning enthusiasts such
as Dr Richard Seed, an American scientist who followed the announcement
of Dolly's creation by setting up a programme to create the first human
clone.
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- He believes that cloning could become a legitimate treatment
for infertility and could enable bereaved families to replace lost loved
ones. Spin-off technologies could help to slow or reverse human ageing
by replacing old body parts with cloned new ones.
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- Campbell, who has moved to take up a new post at Nottingham
University, said: "The only real clones are identical twins and anyone
who really knows twins understands that even they have different features
and personalities."
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