Identity Crisis: The Murder, the Mystery, and the Missing DNA (Kindle Single) by Jefferson Bass

Author:Jefferson Bass [Bass, Jefferson]
Language: eng
Format: epub
Publisher: HarperCollins
Published: 2015-04-27T16:00:00+00:00

Chapter Three

Twisted Ladder, Twisted Case

THE AIRPORT SECURITY screener peered closely at the two small objects in the envelope I had taken from my pocket. After a moment he called over another screener, and then another, and then a supervisor. Within minutes I was surrounded by armed Transportation Safety Administration guards who questioned me closely about the two human teeth I was carrying—my “carrion luggage,” to make a terrible pun. Luckily, I was on my home turf—Knoxville’s McGhee-Tyson Airport—and half the TSA guards there knew me. They weren’t questioning me because they were suspicious; they were questioning me because they were curious. After I had explained why I was flying to Texas with two teeth from a dead woman in my pocket, they waved me on and wished me luck in San Antonio, the next stop in my quest to determine, once and for all, whether 05-01 was Leoma Patterson after all. Like a runner in a relay race—a scientific race to find the truth—I was about to pass the baton to the next runner. In this case, the baton I was handing off consisted of the two teeth, and tucked inside those teeth, I hoped, was enough mitochondrial DNA to settle the matter.

Millions of people first learned of the forensic potential of DNA during the televised murder trial of O.J. Simpson. Blood from the scene where Nicole Simpson and Ronald Goldman were slaughtered—a sidewalk leading from Nicole’s condominium—matched O.J. Simpson’s blood type and DNA, a parade of prosecution witnesses testified. In addition, blood matching Nicole’s DNA was found on a pair of socks in O.J.’s bedroom, and blood matching Ron Goldman’s DNA was found in O.J.’s Bronco. The odds against anyone other than O.J., Nicole, and Goldman being the sources of those bits of blood-borne DNA were astronomical, experts explained, ranging as high as nearly one in ten billion.

The reason for such overwhelming mathematical probability, the jury learned during days of mind-numbing scientific testimony, is the immense size of the DNA molecule, coupled with the near-infinite ways in which its biochemical building blocks can be arranged. Its now-famous shape, called a double helix, resembles a ladder whose uprights have been twisted so they spiral or corkscrew around one another. The three billion “rungs” of this corkscrew ladder consist of pairs of chemical bases named adenine, guanine, cytosine, and thymine (abbreviated A, G, C, and T). For biochemical reasons I won’t go into (because I don’t begin to understand them!), every “rung” with an A on one side always—no exceptions—has a T on its other side; similarly, G is always paired with C. So if you were magically reduced to the size of an atom, and you began climbing this three-billion-rung ladder, the first five rungs you ascended might be constructed this way: AT, TA, CG, TA, GC. Think Legos—billions of Legos—spiraling miles into the sky.

Statisticians and evolutionary scientists have an old saying about monkeys and typewriters that’s meant to illuminate how random variation, given enough time, produces specific meaning. One

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