Having cloned sheep and who knows what else, wouldnt it be a good idea for scientists to begin cloning the worlds endangered species? Is there any reason not to?

Cloning technology has improved dramatically since 1996 when Dolly the sheep became the first mammal to originate from a somatic cell (any cell of a living organism other than the reproductive cells). We now have a better understanding of nuclear reprogramming, a process that gives a cell the capacity to generate all the different types of cells that make up the organism called totipotency. As a result, many species have been successfully cloned, including those of amphibians, fish, insects and mammals. But cloning is still inefficient, with a maximum of 5 per cent of cloned embryos developing into healthy offspring.

There have been several attempts at cloning endangered or even extinct species, such as the gaur and the Pyrenean ibex. These have been largely unsuccessful. Generally, hundreds of embryos have to be created, of which only a handful can be implanted. And of those, only a couple are born, but these often die soon after birth.

The problem in most cases is sexual isolation, which is part of the speciation process, in which one species eventually evolves into two separate ones. These become incapable of reproducing with each other because their reproductive cells are no longer compatible or the embryo of one species cannot be carried by a mother of the other. Both issues affect cloning.

One species where cloning has been successful is the African wildcat. Although wild, this species is still genetically close enough to the domestic tabby for interspecies embryo transfer to be slightly more efficient. More importantly, cloned animals were then able to mate and reproduce among themselves.

But the main problem with cloning remains: it eliminates genetic diversity. The whole point is to reproduce an exact copy of an individual, such as a champion racehorse. Most higher organisms, however, reproduce sexually, which leads to the offspring bearing a combination of characteristics from both parents. This genetic mix and match allows species to adapt to their environment and reduces negative traits or diseases within the population. A diverse genetic pool is essential for a species to survive in the wild.

So although cloning might help preserve some species in critical times, the best way to avoid their extinction is to protect their environment and stop senseless poaching of wild animals.

Alena Pance, Wellcome Trust Sanger Institute, Cambridge, UK

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Cloning to the rescue - New Scientist