Explainer: DNA hunters

DNA display
DNA display

Scientists can extract DNA (parts of which are displayed on screen) from samples they picked up in the environment. They then look for patterns in this genetic material to identify which species had left it. In this way, biologists can “detect” what organisms had been around.

“Traces of DNA are left behind by every species everywhere,” says Ryan Kelly. He is an ecologist with the University of Washington at Seattle. He also works at the Center for Ocean Solutions at Stanford University in Palo Alto, Calif. Scratch an itch, he says, and you shed skin cells containing your DNA. Pets and other animals leave behind bits of dead skin known as dander. Reptiles shed skin as they grow. There’s even DNA in poop.

“Just like forensic scientists do at a crime scene every day, we are detecting that trail of DNA that’s left behind,” explains David Lodge. He’s a biologist at the University of Notre Dame in South Bend, Ind. And he hunts for signs an animal has been around by scouting for bits of the DNA it had shed. Scientists refer to this genetic litter as e-DNA. Here, the “e” stands for environmental.

DNA strand
DNA is shaped like a twisted ladder. Its rungs are made of what are known as base pairs. There are four types.

DNA is the genetic material found in the cells of all living organisms. It looks like a long, twisting ladder. Each rung on that ladder is a pair of chemicals called nucleotides. There are four of these chemicals: adenine, thymine, cytosine and guanine. Scientists refer to them as A, T, C and G, for short. Each nucleotide on one long side of the ladder must pair with a specific one on the other side. A’s only pair with T’s. Any C’s must pair with G’s.

Humans have about 3 billion rungs, or base pairs,…

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