Sequence and rewind: Scientists are racing to clone the extinct woolly mammoth and other prehistoric beasts, perhaps one day creating a real life 'prehistoric zoo'.

Credit: AFP

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The naysayers were finally proved wrong only last month. DNA from our closest ancestors, the Neanderthals, was not only discovered uncontaminated, but was also successfully sequenced.

Discovering 80-million-year-old DNA might be a stretch, but 38,000-year-old DNA is achievable. Edward Rubin, from the Lawrence Berkeley National Laboratory in California, developed a method of targeting specific sequences in DNA. His team sequenced a total of 65,000 base pairs, recovering 29 of the 35 genes they targeted. Scientists expect the entire genome to be sequenced within two years.

The technologies that made it possible are very recent developments. While reflecting on the new developments in DNA sequencing, Rubin commented that "we're poised to see technological advances that will enable us to do things tomorrow that today don't seem so feasible."

While some scientists work towards reconstructing ancient DNA, others are focusing on the unique problems that arise when a surrogate mother from a closely related species is used during the cloning process.

A cloned animal receives the DNA from the nucleus of a normal body cell, which codes for the development of most structures and processes in the body. But mammalian cells contain two distinct genomes: one in the nucleus, and another genome that exists only in the cell's powerhouse, the mitochondria.

These minature organs, once free-living bacteria before they were 'ingested' by other early cells, are the component of a cell that converts sugars into ATP - the universal energy currency of the body. Mitochondrial DNA codes for about 13 proteins necessary for ATP production.

In mammals, the mitochondrial DNA is passed from mother to offspring without any changes, except for random mutations. The mitochondrial DNA in sperm is destroyed by the egg during fertilisation.

A recent study set out to determine whether the same process would occur when a macaque (a type of monkey) embryo was created using an egg from a rabbit. Surprisingly, the mitochondrial DNA from both species survived as the embryo began to develop into a macaque.

Debates in the scientific community continue as studies like these raise questions about hereditary. Are clones with a mother from a different species a true copy? Does it matter? What about the natural bacteria in the gut, passed from mother to offspring? How would a monkey, whose mother was a rabbit or a baboon, fare outside a zoo?

If a jury existed for these matters, it would still be out. While other areas of science and society have had hundreds of years to develop sophisticated philosophical arguments, genetic engineering uncovers novel ethical issues on a seemingly daily basis.

As scientists question the ethics of creating and resurrecting animals, animal activists also worry that cloning may replace large-scale conservation. "Now is the time … to ask how much of our limited resources should be devoted to seeking biotechnology-based solutions to conservation problems," wrote David Ehrenfeld of Rutgers University in the U.S., in an essay on vertebrate cloning published earlier this year in the U.S journal Conservation Biology.

Ehrenfeld considers cloning a glamorous technology with the potential to create a false impression of an easy, high-tech solution to the ongoing problem of extinction. It is also an expensive process, likely to be biased toward cloning animals that would become zoo or theme park attractions. "The cloning of endangered rays, caecilians [snake-like amphibians] or vipers may have to wait until we have done the showier rare birds and animals," according to Ehrenfeld.

While one argument says it is appropriate - even necessary - to bring back unique animals that humans have driven to extinction, other arguments which are equally valid maintain that it is unethical to 'play god' by resurrecting two of every kind. This may be one situation where the limits of science are, perhaps, less of an issue than the limits of our own ethics.

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