杏吧原创

IT鈥橲 SAFE to clone primates, including humans, but not mice, rats, sheep,
cows, pigs and opossums, claim geneticists. They says there is a vital genetic
difference separating the clonables from the unclonables.

鈥淚t lays to rest some of the technical worries about cloning,鈥� says Randy
Jirtle of Duke University in Durham, North Carolina. But other researchers say
the claims are dangerous.

鈥淭he authors have allowed themselves to over-interpret their interesting
results,鈥� says Ian Wilmut, creator of Dolly the sheep. 鈥淚 hope that this will
not be used to give encouragement to those who wish to clone humans.鈥�

Cloning often fails because of 鈥渓arge offspring syndrome鈥�, in which animals
grow too big in the womb and often die at birth. Jirtle and his colleagues say
this is because a gene called IGF2R that slows growth can get switched
off.

In most mammals, including all those cloned so far, the paternal copy of
IGF2R is 鈥渕othballed鈥� in a process known as imprinting. If the remaining
maternal copy is accidentally switched off during cloning, nothing prevents
large offspring syndrome.

After analysing tissue from an array of mammals, Jirtle found that in
primates neither copy of IGF2R is imprinted鈥攐r imprintable.
鈥淲e鈥檝e got two brakes, whereas most cloned animals have one, and our brakes
can鈥檛 be altered,鈥� he says.

鈥淏ut to say this makes cloning safer is a ludicrous claim,鈥� says Robin
Lovell-Badge, a cloning specialist at the National Institute for Medical
Research in London. Disruption of other imprinted genes might be just as
important, he says.