Who could forget that day, that 9/11 day in 2001, when roughly 3000 lives were snuffed out? The remains of so many loved ones could be counted in grams. So many families wanted some satisfaction, knowing that they had some small part of a victim to honor and bury.

Soon after the tragedy the call went out for relatives and friends to submit tooth brushes, hair from combs, banked sperm and egg samples, or any cellular material that might have belonged to their loved one who perished in the most horrendous terrorist attack in the history of New York City. This was the start of the long process of matching the fragmentary remains of those victims with their known cellular samples.

             The DNA detectives went to work. One of the processes they used for analysis was to type the mitochondrial DNA of victims’ samples. Mito. . .what, you ask? Maybe, if you were really paying attention in your high school biology class, you remember what mitochondria are. Or, you might remember them from Madeleine L’Engel’s lovely book, “A Wrinkle in Time”.

                Mitochondria are tiny (of course) structures found in cells. Besides their function of converting sugar (glucose) to a usable form of energy (ATP), mitochondria have their own DNA. Most of the DNA that allows cells to divide and impart traits to the next generation is located in the nucleus of the cell. Mitochondrial DNA is also inherited through cell division, but inheritance of this DNA is special in that it is passed through the maternal line. This occurs due to the fact that the new individual (Miss Pratt’s bio class again) results from the union of a sperm cell and an egg cell. Sperm cells contain a nucleus, but no other cell parts, just a bag of DNA with a tail. Egg cells contain lots of mitochondria-rich material surrounding the nucleus.

                Mitochondrial DNA is far simpler than nuclear DNA, occurring as a simple ring. There are fewer genes, and it is less complex to sort the genes into the genetic variations that occur in the population. Here’s the really significant factor that makes mitochondrial DNA so useful. Unlike nuclear genetic material, which undergoes a good deal of shuffling during sexual reproduction, mitochondrial DNA remains intact from generation to generation, going from mother to child.

                The only changes in these genes results from mutations, which occur at a regular rate, and therefore can be a predictor of the age of genetic material. The more mutations there are, the older the sample.  In1987 Wilson, Cann and Stoneking at the University of California proposed the theory of the Mitochondrial Eve. This theory said that all mitochondrial DNA can be traced to one ancestral woman, or Eve. By analyzing DNA samples from populations around the world, and counting the number of mutations, it was found that the oldest human populations came from Africa about 200,000 years ago.

                What does the “Eve” have to do with solving forensic mysteries? The remains from the Twin Towers site analyzed at a special lab at the Fresh Kills landfill on Staten Island could be identified, not just from hair and cellular material that may have been left behind by the victims, but also by correlating the DNA in the remains with their mother’s DNA.

                The process of identifying the genetic variations, or in terms of DNA analysis, fragment lengths, is the same as what has been described in my article, “When Is a Fingerprint Not a Fingerprint?”, in last month’s newsletter. It is less complicated only because there are fewer genes to analyze and variation in these genes is usually stable from one generation to the next. Remember, mutations happen over time. Although there is usually more mitochondrial DNA in the remains, these processes are nevertheless lengthy and expensive.

                As the DNA codes in genes are analyzed further, more “quirks” in their inheritance will be isolated and utilized for identification purposes. Thanks to mitochondrial DNA analysis, many victims of the tragedy of 9/11 have been identified, helping their families to put them to rest.

The following resources give good accounts, explanations and diagrams of the processes described above.

“Criminalistics, an Introduction to Forensic Science” Third Edition, Richard Saferstein, Pearson/Prentice Hall, 2007, ISBN 0-13-221655-8.

“DNA Technology, the Awesome Skill”, I. Edward Alcamo, Wm. Brown Publishers,1996,  ISBN 0-697-21248-3.