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DNA Detective

When crime threatens rare animals, a scientist turns sleuth to crack the case

By Jacqueline Adams | May 8, 2006

A U.S. Fish and Wildlife Service officer was at the crime scene: John F. Kennedy International Airport in New York City. He'd just seized a shipment of handbags and shoes he suspected were made from skins of a threatened species of crocodilian. Importing products made from legally protected animals is against the law without a permit.

But the importer claimed the officer had it all wrong. He insisted that the products came from an unprotected animal species with a similar skin pattern as the endangered crocodilian. The officer didn't buy the importer's claim, but he lacked evidence to prove his hunch. Would the importer get away with the crime?

For help, the officer turned to George Amato, a conservation geneticist who studies natural history and endangered species. When the need arises, his genetics lab at the American Museum of Natural History in New York City becomes a forensics lab for studying crime-scene evidence. Could he crack the case?

DNA Detective

When the evidence—crocodilian handbags—arrived at his lab, Amato wasn't fazed by the importer's claim that skins from different species look alike. He knew for sure he would be able to identify the animal that was used to make the handbag. That's because skin cells, like all body cells, contain the animal's DNA, or hereditary information. DNA is made of four different chemicals called nucleotides, which can string together in billions of different sequences. Every species has a unique DNA sequence for certain genes (units of hereditary material). So if Amato could read the sequence, he'd prove which croc had been bagged.

Fortunately, he wouldn't have to read the entire sequence, which contains 2.5 billion nucleotides. He could find the information he needed in a short DNA section called the barcode region. This section of DNA works like the black and white barcodes on products sold in stores. Store scanners can identify billions of different items based on how a few bars are arranged. Likewise, says Amato, "A relatively small piece of DNA from a particular region has enough differences that it effectively acts like a product barcode for species."

Cracking the Code

After Amato extracted DNA from the skin cells that made up the crocodilian handbag, he started a chemical reaction that built copies of the barcode region. Multiple copies made it easier for a machine called a DNA sequencer to read the code. This ability to amplify, or copy, DNA means that scientists can read the barcode even if they have only a tiny piece of the animal. In fact, Amato has solved cases in which the only crime scene evidence was a single hair. "Theoretically, all I need is one cell," he says. "That's why this technology is so powerful for forensics."

Once he had the barcode sequence, he needed to determine to which species it belonged. He searched a computer database of sequences and found a perfect match-the Yacare caiman, a threatened species of South American crocodilian! Amato phoned the U.S. Fish and Wildlife Service officer, who then started a criminal investigation against the importer.

Researchers hope to someday develop portable equipment for reading DNA barcodes right at the crime scene. Amato says, "This will be something similar to the way you scan a barcode at a grocery store." That would enable officers to identify and arrest importers of threatened species on the spot.

Meanwhile, Amato's lab tackles 20 to 25 wildlife CSI cases each year. The illegal products he has helped keep off the market include seal skins, shark fins, and whale and monkey meat. When the results come in, he has mixed feelings. "On one hand, it's sad to know that an endangered or protected animal was illegally harvested," he says. "On the other hand, it is rewarding to play a role in closing down that illegal activity."

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