It sounds simple, test the DNAs and see if they match, right?
Not that simple. It is easy to separate fertilized eggs (aka embryo cloning - for human being, it divides into as many as 32 embryos) and create identical twins (in theory one can create at most 32 twins this way). Then one can grow one cell to create the "mother" of Snuppy, and freeze the others to become he daughter Snuppy by waiting for a few years. The DNA are exactly the same but they are really identical twins.
However, if Snuppy is cloned, only the DNAs inside the nucleus are identical. There are DNA strain in the mitochondria. They do not contribute much to the organism's genetic information. But they come from the donor egg (which is different from that of the 'mother'). So the scientists tested both DNAs.
"We received blood samples from the donor dog Tai, the clone Snuppy and the surrogate mother who is a Labrador retriever," explained canine geneticist Dr Elaine Ostrander
"We prepared DNA from those samples and then we tested them in two ways."
The team looked at DNA in the cell nucleus and in mitochondria, components of the cell's outer structures.
They found that only Snuppy's nuclear DNA matched with the donor dog, as expected. Snuppy's mitochondrial DNA did not match with the donor dog; this genetic material does not come from the animal being copied, but from the egg into which donor DNA is inserted.
"The data really supports the notion that Snuppy is a clone of Tai, and that Snuppy was developed using the technical approaches that the authors suggested in their paper," said Dr Ostrander.
Therefore, it is concluded that Snuppy is innocent.
p.s. the technology of creating and 'archiving' identical twins leads to another controversy: i.e., can one create a back-up child before a child is born? (So that one can grow the frozen egg many years later, e.g. if the child dies of accident)