Just what is "Jewish DNA," anyway? There is no scientifically acceptable standard for Jewish DNA. Dr. Robert Pollack, a professor of biological sciences and director of the Center for the Study of Science and Religion at Columbia University, makes the following important observation in his online article, "The Fallacy of Biological Judaism" (Pollack, 2003):
If there is no genetic marker that can identify a person as a Jew, I would ask Thomas Murphy and other critics of the Book of Mormon exactly what DNA evidence we should be looking for to test the hypothesis that a tiny handful of Hebrew people entered the Americas in 600 B.C.? What can be challenged is the once-common LDS assumption that the Book of Mormon told the whole story of the origins of the Americas, but it's much more reasonable to understand that it's only part of the story. Given the way genes diffuse, it is possible that every Native American was in some way a descendant of Lehi, but there is no need to assume that his Y chromosomes - whatever features they had - are still around in large numbers waiting for scientists to puzzle over all the "Jewish DNA" in the Americas. (And of course, if markers related to "Jewish DNA" were found among Native Americans, wouldn't it immediately be assumed to have come from mixing with Europeans? I think the answer is yes.)
Unlike asking "Are Jews a family?", as historians have traditionally done, geneticists seeking to advise Ashkenazic families are also, in passing, asking, "Do Jews all share the same versions of one or more genes?" -- a question with a testable, precise answer. As no two people except pairs of identical twins have exactly the same version of the human genomic text, this claim could be confirmed or rejected by a search for versions of the human genome shared by all Jews and no other people.
Given the historical context of the Nazi "experiment," it is all the more remarkable that Jews all over the world have been flocking to the new technology of DNA-based diagnosis, eager to lend their individual genomes -- each a surviving data point from the terrible experiment in negative selection -- to a revisiting of this issue of biological Judaism.
At a recent meeting of the Association of Orthodox Jewish scientists and the Columbia Center for the Study of Science and Religion, it became clear that Jewish curiosity has provided sufficient genetic material to give a perfectly clear negative answer: There is no support in the genomes of today's Jews for the calumnious and calamitous model of biological Judaism. Though there are many deleterious versions of genes shared within the Ashkenazic community, there are no DNA sequences common to all Jews and absent from all non-Jews. There is nothing in the human genome that makes or diagnoses a person as a Jew.
By the way, there might be some evidence of pre-Columbian Middle Eastern and European genes entering the Americas based on an analysis of human lymphocyte antigens (HLAs). The article I'm thinking of is not in established journals, which leaves a big question mark over the work, but that doesn't necessarily condemn it. Look at the work of James L. Guthrie and let me know what you think.