The emerging genetic picture is based largely on two studies, one published two years ago and the other this month, that together show that the men and women who founded the Jewish communities had surprisingly different genetic histories.

The earlier study, led by Dr. Michael Hammer of University of Arizona, showed from an analysis of the male, or Y chromosome, that Jewish men from seven communities were related to one another and to present-day Palestinian and Syrian populations, but not to the men of their host communities.

The women's identities, however, are a mystery, because, unlike the case with the men, their genetic signatures are not related to one another or to those of present-day Middle Eastern populations.