Carnivorous Nights_ On the Trail of the Tasmanian Tiger - Margaret Mittelbach [15]
It was mind-boggling, thrilling, and slightly disturbing. And given the pace of biotechnology—the mapping of the human genome, gene ther-apy—it seemed well within the realm of possibility. “So, within twenty years or so, will cloning extinct species be routine?” we asked. We imagined a zoo of once extinct animals: dodos, passenger pigeons, woolly mammoths.
Don looked at us as if we were the mad scientists. “We have to mitigate the enthusiasm with the reality of what we're doing,” he said gently.
DNA is not life, he reminded us. It's a blueprint for life, meaning that it tells a life, an organism, what species it will be, what it will look like, how it will grow. Sometimes it tells an organism how to behave or what its disposition will be. Because DNA is itself inanimate and made up of chemicals, an organism's DNA can survive well after death, sometimes for thousands of years.
Retrieving thylacine DNA was the cloning team's first task. Because the tiger pup was so old, dating from the mid-nineteenth century, it was preserved in ethyl alcohol (ethanol) rather than formalin as more recent specimens would be. (Formalin, a preservative that came into vogue around the same time the pup was pickled, destroys DNA; ethanol doesn't.) The scientists took samples from the tiger pup—from its organs, muscle, and bone marrow—and then extracted hundreds of thousands of DNA strands. In the media, the extraction was hailed as a triumph. Later, upon analysis, however, the DNA was found to be contaminated. It was a bit awkward. The pickled tiger pup had figured prominently in the press as the key to bringing the thylacine back to life—and the museum had already announced that the extraction had been successful. But what could they do? They were scientists, not sideshow barkers. They began to look at other tiger specimens in the collection. The museum owned thylacine pelts, organs, bones. Ultimately, the cloning team extracted DNA from a thylacine femur and molar. It was good—in thousands of fragments—but they could work with it.
The next step was making sure they had all the correct bits and pieces of the tiger's DNA. They still needed to figure out how many chromosomes the tiger had and what was in them. Later, they would reassemble the DNA, like the pieces of a jigsaw puzzle. Karen led us over to her computer terminal. It was awash with graphs and symbols, documenting the tiger's life code.
When—if— they were able to re-create the tiger's entire genome (which in itself would be an incredible scientific achievement, Don pointed out), they would be ready for the ultimate stage of the project: cloning a tiger.
“Of course, having just one wouldn't do any good,” Karen said. “We'd have to make at least two hundred tigers.” Then she and Don began to laugh. Even in the heart of the cloning project it seemed like science fiction.
“There's really a lot of pressure,” said Don, still laughing and wiping tears from his eyes. The chances of success—of creating just one thylacine— were 5 to 8 percent in twenty years.
But, he added, the odds could get better. Technology was improving all the time. Since the discovery of the structure of DNA in 1953, scientists have learned to dissect, copy, map, manipulate, and even change the code of life. Through genetic modification, they've created insectresistant breeds of corn. Tomatoes that have extended shelf lives. They have bioengineered cows to produce “farmaceuticals,” including potential treatments for blood clots, anemia, hemophilia, and emphysema. They have put bioluminescent jellyfish DNA into white rabbits to make them glow under ultraviolet light—and they have even introduced spider DNA into goats, causing them to produce copious amounts of superstrong silk webbing in their milk.
Cloning, or bringing to life the twin of an individual, has also become a reality. The first mammal clone, Dolly the Sheep, was created in 1996 from a single cell nucleus taken from the