My two-year-old has a pair of pajamas that glow in the dark. He loves them, and asks to wear them almost every night. And I say yes - as long as they're clean. But what do I say when he asks me for a glow-in-the-dark puppy?

Scientists at Seoul National University in South Korea recently announced the successful cloning of the world's first transgenic dog. "Transgenic," meaning that the dog, dubbed Ruppy (a combination of "ruby" and "puppy"), carries a gene from another species - in this case a red-fluorescing protein taken from a sea anemone. Headed by Byeong-Chun Lee, who made headlines in 2005 with Snuppy, the world's first cloned dog, the team of scientists injected cloned canine cells with the fluorescent gene in order to create Ruppy and four other glowing beagles. Ruppy doesn't actually glow in the dark, but she does fluoresce an eerie-looking red under UV light (see right).

I've seen fluorescing anemones at aquariums, waving in the water, their delicate fronds emitting a soft light alongside plaques explaining the gene they carry that makes them glow. And I can't help thinking about these creatures - hidden in the ocean for ages before being discovered by humans - glowing for perhaps no reason other than the glory of their Creator.

Now we have not only seen the fluorescing sea anemone, we have isolated what makes it glow, harvested the gene, and successfully implanted it into a mammal. We've made ourselves a glowing dog, though I doubt my son will be getting his glow-in-the-dark puppy any time soon - only 1.7 percent of the cloned embryos from which Ruppy hails developed to full term.

Besides, Ruppy wasn't engineered for the commercial market anyway. The implications of transgenics extend not only to medicine but to industry and agriculture as well. Although two other species of transgenic mammals have previously been created - mice and rabbits - transgenic dogs could be of particular use to researchers. Dogs, especially lab beagles, react to certain drugs in ways very similar to humans, and thus can be used to predict human responses in clinical drug trials.

I can't help wondering, though, as we push the boundaries of current scientific limitations, how far we will - or should - go. Ruppy is a far cry from the genetically engineered humans of futuristic movies like Gattaca; at the same time, I wonder if Ruppy represents a step toward that. We're not close enough for me to fear the day when parents will choose their children's hair or eye color, but as we inch ever closer, I worry about the degree to which we meddle in things we still don't fully understand.

A fluorescing puppy is interesting, and I appreciate the potential for future scientific discoveries that will benefit people. But I also fear the potential ramifications of genetic engineering, as it moves from less of a sci-fi fantasy into a reality.

How about you?