With Hwang's scientific credibility in shambles, the status of the world's most famous dog hangs in the balance. The embattled scientist maintains that Snuppy is the world's first canine clone, and he even hired an independent Korean DNA lab, HumanPass Inc., to verify that assertion. The verdict: HumanPass CEO Seung Jae Rhee told TIME last week, "There is no dispute about these results, and so I am 100% certain on Snuppy's authenticity." But since HumanPass is in essence working for Hwang, that's hardly good enough for the investigative panel at Seoul National University, which is carrying out independent tests, or for the editors of Nature, who have ordered an investigation.
If Snuppy really was cloned from the ear cell of a 3-year-old male Afghan named Tai, it shouldn't be tough to prove, even to those outside investigators. As long as they have tissue samples from both the clone and the parent, they should be able to determine whether DNA in the nuclei of both animals' cells is identical--the first hallmark of a true clone. Ian Wilmut, the Scottish scientist who created Dolly the sheep in 1996, had to provide such samples to prove to skeptics that he had created history's first mammalian clone.
Even with the controversy raging over his stem-cell paper, Hwang could have forestalled some of the questions about Snuppy if he had offered one additional bit of confirming proof in his original paper in Nature. That piece of critical evidence comes from the animals' mitochondria, tiny energy-producing structures within each cell. While most of a mammal's DNA resides in the nucleus, there's also some in the mitochondria. (Nuclear DNA forms the animal's basic genetic blueprint; mitochondrial DNA contains instructions for making proteins involved in various metabolic functions within the cell.)
Mitochondrial DNA is passed down from the mother as part of the egg's genetic contribution. Identical twins, for example, have the same nuclear and mitochondrial DNA, since they're produced when a single egg is fertilized and the resulting embryo splits in two. With a clone, the situation is different. Because the cloning process that Hwang says he used to create Snuppy involves two dogs--one for the nucleus and another for the egg--Snuppy's mitochondrial DNA should not match Tai's. That's what Rhee's scientists say they've found and what Hwang undoubtedly hopes the university and Nature will find as well. Final, ironclad proof of Snuppy's provenance would involve showing that the dog's mitochondrial DNA matches that of his egg donor. It's not clear, however, whether that test is being done.