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have set up shop in the chromosomes of an unintended host.”
    The absolute silence of the listeners in the room confirmed to Sullivan that she had their attention. “Mr. Doumani will now explain the process in detail.”
    A very astonished Azrhan Doumani, who obviously didn’t expect to be called on so soon, hesitantly got to his feet, swallowed a few times, and stated, “When Dr. Sullivan came back with her samples, we first treated each of the specimens to a shot of liquid nitrogen, freezing them into a brittle solid that we can easily grind to a fine mash using a mortar and pestle.”
    “We also go for the dry ice effect,” Sullivan interjected with a wink to her nervous colleague. “White vapors billowing out of beakers and rolling over the lab bench—it makes for great visuals whenever the media’s around.”
    The quip brought a few chuckles, but more important to Sullivan, she saw her young protégé’s shoulders relax a notch.
    “We then reach into the geneticist’s toolbox,” he continued, his manner less stiff than before, “take out a concoction of chemical washes called C-Tab, add them to our ground-up powder through a complex series of steps, and, after a spin in the centrifuge, end up with a solution of pure chromosomes—the gene strands of the organism—floating above all the debris. We siphon this off, again reach into our bag of tricks, this time to pull out what geneticists use to cut and paste DNA— restriction enzymes. We add them to our solution, where they break the chromosomes into genes and the genes into even smaller strands of DNA suitable for testing. Each enzyme attacks a specific site on the chain, and in this case, we treated our samples with the enzymes that would break off among other things pieces of DNA from a cauliflower mosaic virus, or CaMV. This is the most common invasive organism used in genetic engineering. Our idea was to look for DNA fragments from it, reasoning that by demonstrating their presence we’d have confirmation of a vector’s having infected the vegetation we were testing.”
    He paused, taking a sip of water, and Sullivan used the moment to gauge the audience’s interest. Several chairs squeaked, there were a few coughs, but tape recorders continued to roll and pens remained poised in midair, ready to write. Good, he’s still got them, she thought, breathing a sigh of relief, because unless they understood the test process, they wouldn’t grasp the real story hidden behind it all.
    Doumani continued. “Searching for and identifying these fragments amongst all the rest involves a few more of the standard procedural tools of our trade—separating out the various pieces of DNA on an electrophoretic gel, locating them by using a hideous carcinogen called ethidium bromide, which turns them pink, then literally giving them a scrub with a wash called GENE CLEAN— until we’re finally ready to lift a genetic fingerprint from them. Now, whether we’re after a drop of blood at a crime scene or a vector in plants, the identification technique involves the most basic tool a geneticist uses— stock DNA preparations called primers. When we add a specific set of them to strands of DNA, they line up and lock on to the portions of the strands where the nucleic acid sequences are exactly complementary to their own. In other words, for our purposes here, we can use these primers as probes, to find whether a particular type of DNA is present in the chain we’re studying, provided we know what to test for. In this case, since we could only make an educated stab at what they used in the vectors, we also were guessing about what primers to employ, again settling on those for the cauliflower mosaic virus.” He paused again.
    No one made a sound.
    Still so far so good, thought Sullivan.
    “We heated each tiny specimen of DNA we were testing to near boiling,” resumed Doumani, “ninety-four degrees centigrade exactly, to break the DNA’s double helix structure into