The four mitochondrial lineages common among Ashkenazis are now very rare elsewhere in the Near East and Europe, making it hard to identify with certainty the lineages from which they originated.

With the entire mitochondrial genome in hand, Dr. Richards could draw up family trees with a much finer resolution than before. His trees show that the four major Ashkenazi lineages in fact form clusters within descent lines that were established in Europe some 10,000 to 20,000 years ago. The same is true of most of the minor lineages.

“Thus the great majority of Ashkenazi maternal lineages were not brought from the Levant, as commonly supposed,” Dr. Richards and colleagues conclude in their paper. Overall, at least 80 percent of Ashkenazi maternal ancestry comes from women indigenous to Europe, and 8 percent from the Near East, with the rest uncertain, the researchers estimate.

Dr. Richards estimates that the four major lineages became incorporated into the Ashkenazi community at least 2,000 years ago. A large Jewish community flourished in Rome at this time and included many converts. This community could have been the source of both the Ashkenazim of Europe and the Sephardim of Spain and Portugal, given that the two groups have considerable genetic commonality, Dr. Richards said.

Doron M. Behar, of the Gene by Gene company in Houston and a co-author of the 2006 survey, said he disagreed with Dr. Richards’ conclusions but declined to explain his reasons, saying they had to appear first in a scientific journal.

David B. Goldstein, a geneticist at Duke University who first detected the similarity between the founding mothers of Jewish communities and their host populations, said the new analysis was well done but that the estimate of 80 percent European origin for the Ashkenazi maternal lineages was not statistically justified, given that mitochondrial DNA lineages rise and fall in a random way.

A recent analysis based on the whole genomes, not just mitochondrial DNA, of Jewish communities around the world noted that almost all overlap with non-Jewish populations of the Levant, “consistent with an ancestral Levantine contribution to much of contemporary Jewry.” Dr. Richards said that the finding was compatible with his own, given that the Levantine contribution was not that great.