午夜福利1000集合

WHAT should you do when a beloved pet dies? Resign yourself to its
loss鈥攐r try to bring it back to life by ordering a genetically identical
copy?

That鈥檚 the choice facing pet owners after the creation of the first kitty
clone. 鈥淭o some people, the need to replace a pet is psychologically the same as
replacing a child,鈥� says Herb Neiburg, director of behavioural medicine at Four
Winds Hospital near New York. The difference is that pet cloning doesn鈥檛 evoke
the condemnation that goes with human cloning. But whatever the species, people
who think cloning will resurrect their loved ones are bound to be
disappointed.

That hasn鈥檛 stopped companies in the US from storing tissue samples for
people who want to clone their pets. One of them, the wryly named Genetic
Savings & Clone of Texas, owns the commercial rights to the cat-cloning
technique. It says that if all goes well it will offer cloning services to a few
clients within the year.

鈥淲e try to make it clear to them we can鈥檛 resurrect their animal,鈥� says
general Charles Long. 鈥淭he best we can do is make a genetic duplicate.鈥� Long
claims the company turns away customers who believe that cloning can recreate
their pet.

But Neiburg, who counsels people grieving for pets, fears that such warnings
may not be enough. When normal replacement pets don鈥檛 live up to an owner鈥檚
expectations, he has seen people abuse or abandon them. And with an expensive
clone, expectations will be much higher. Cloning companies, he says, should
provide their clients with professional counselling to determine whether
advanced reproductive biology is really the answer to their emotional
distress.

cc the kitten鈥攖he cc stands for carbon copy鈥攃ertainly represents
a milestone. Several groups have been struggling to clone cats for over a year.
And while cat cloning could in theory help preserve endangered species, cc will
go down in history as the first animal to be cloned with the aim of satisfying
people鈥檚 emotional needs, rather than for medicine or agriculture.

The rub is that those needs are about duplication, and cc doesn鈥檛 look
exactly like her genetic donor. She was cloned from a tortoiseshell cat, a breed
whose three-colour coat pattern is not determined purely by genetics, but also
by environmental factors and a random process called X-chromosome inactivation.
But even more importantly for pet owners, such factors also mean that clones are
likely to behave differently to their genetic parent.

And success may be hard to repeat. To clone any animal, researchers suck the
genetic material from an egg and replace it with the nucleus of a donor cell. To
make cc, about 200 such nuclear transfers were carried out. Of the resulting
embryos, only 87 matured enough to be implanted in surrogate mothers. Just two
pregnancies were established, and only cc went to term.

Mark Westhusin of Texas A&M University at College Station says his team鈥檚
success could mean they鈥檝e hit on a reliable recipe for producing cat
clones鈥斺�漮r maybe the gods just smiled on us that day鈥�. And while 84 of the
implanted embryos were created from skin cells, cc鈥檚 genetic material came from
a cumulus cell. Such cells, which surround developing eggs, are hard to obtain
and found only in females.

The copy cat has also arrived when concern is growing about the safety of
cloning. A recent study of mouse clones, for example, revealed subtle genetic
problems that are hard to detect and may shorten lifespan. cc looks healthy now,
but her creators have yet to carry out any detailed examinations.

Animal welfare groups are not impressed. Why pay a huge sum for a clone that
may have problems later in life, they ask, when on the day cc was born 6000
unwanted cats were put down in the US alone.