Excerpted with permission from New Voices, the national Jewish student magazine and part of the network.

The Center for Human Genetics at New York University is filled with the constant hum of busy students, doctors, and patients. There's nothing to indicate that the work researchers are doing here has the potential to radically alter millennia-old conceptions of Jewish peoplehood.

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Incongruous as the setting might seem, though, scientists at the Center for Human Genetics are investigating some of the most fascinating and longstanding questions of Jewish history. Dr. Harry Ostrer, the head of the center, is one of the many scientists around the world using the tools of modern genetic research to uncover the ancient roots of the Jewish people, long the exclusive province of historians. The results of genetic research could have a tremendous impact on the way Jews view themselves and their community.

The recent investigations into Jewish origins are, in some ways, a natural outgrowth of earlier studies of genetic diseases. Jews have long been a favored test group for research on genetic susceptibility to certain diseases. Centuries of living behind ghetto walls and marrying amongst themselves created Jewish populations with relatively homogenous gene pools, making the genetic variations linked to specific diseases easier to spot.

As a medical student at Columbia University in the 1970s, Ostrer, who is Jewish himself, helped to organize a Tay-Sachs screening program in the Bronx. (Tay-Sachs is an inherited syndrome common in Ashkenazi Jews.) As the amount of genetic data he collected grew, he, like many other Jewish scientists, began to wonder what other information might be hiding in his database.

"Eventually," he says, "we developed a rather marvelous database of DNA samples. And then, since we were studying Ashkenazi Jews, we figured 'why not look at other [Jewish] populations as well, and look at origins.'"

Now, many scientists who began their careers studying genetic diseases are employing the same research techniques to delve into the historical roots of the modern Jewish people.

Most of a person's DNA is a unique combination of contributions from that person's mother's and father's DNA. However, in men, the DNA on the Y-chromosome (the male sex chromosome) is inherited only from the father. So a man's Y-chromosome DNA is essentially a duplicate of his father's, his paternal grandfather's, and so on through the generations.

But it's not always an exact duplicate. Occasionally, random mutations will occur in DNA as it is passed from parent to child. If this DNA contains the instructions for something important, say the number of fingers and toes, the mutation could have significant consequences. Fortunately, only about two to three percent of a person's DNA actually contains genetic instructions. The rest has no known purpose and is called "junk DNA." Mutations that occur in the junk DNA are passed on from generation to generation, without causing any harm.

It is these changes in DNA that give scientists a window into the past. The more similar two men's Y-chromosome junk DNA, the fewer generations it must have had to mutate, and the more recently the men must have had a common ancestor. Scientists can find specific combinations of DNA markers, called haplotypes, that are essentially DNA mutations that have been handed down over generations and are indicative of certain population groups. By comparing the haplotypes that are prevalent in two populations' DNA, researchers can tell how closely the two populations are related.

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