Skip to comments.Analysis of Ashkenazi Jewish genomes reveals diversity, history
Posted on 08/26/2010 11:39:53 AM PDT by decimon
Through genomic analysis, researchers at Emory University School of Medicine have shown that the Ashkenazi Jewish population is genetically more diverse than people of European descent, despite previous assumptions that Ashkenazi Jews have been an isolated population. In addition, analyses of disease-related genes of higher prevalence in the Ashkenazi Jewish population indicate that only a minority of traits show signs of positive selection, suggesting that most have arisen through random genetic drift.
The results are published online this week in the early edition of the Proceedings of the National Academy of Sciences.
Investigators in the laboratory of Stephen Warren, PhD, chairman of human genetics at Emory University School of Medicine, used DNA microarray technology to read variant sites across the entire genomes of 471 Ashkenazi Jews. The work comes from a collaboration between Warren and Ann Pulver, ScD, associate professor of psychiatry and behavioral sciences at Johns Hopkins University School of Medicine, who recruited the participants for a study of schizophrenia genetics.
Researchers looked for close to one million single nucleotide polymorphisms (SNPs): common alternative spellings in the genome, analogous to American and British spellings of words such as organize/organise. One measure of genetic diversity in a population is heterozygosity, or how many of the SNPs inherited from the mother and father are different; a more inbred population has less heterozygosity.
"We were surprised to find evidence that Ashkenazi Jews have higher heterozygosity than Europeans, contradicting the widely-held presumption that they have been a largely isolated group," says first author Steven Bray, PhD, a postdoctoral fellow in Warren's laboratory.
The researchers went on to measure linkage disequilibrium, a measure of how "chunky" a population's genomes are. If two individuals from separated groups have children, their descendants' genomes are shuffled by recombination. Successive generations continue the shuffling process, so that the linkage between traits located near each other in the genome is gradually lost over time.
High linkage disequilibrium can come either from an isolated population (for example, an island whose residents are all descendents of shipwreck survivors) or the relatively recent mixture of separate populations. Bray and his colleagues did find evidence of elevated linkage disequilibrium in the Ashkenazi Jewish population, but were able to show that this matches signs of interbreeding or "admixture" between Middle Eastern and European populations.
The researchers were able to estimate that between 35 and 55 percent of the modern Ashkenazi genome comes from European descent.
"Our study represents the largest cohort of Ashkenazi Jews examined to date with such a high density of genetic markers, and our estimate of admixture is considerably higher than previous estimates that used the Y chromosome to calculate European admixture at between five and 23 percent," Bray says.
He adds that his group's analysis agrees with a recently published study from New York University and Albert Einstein College of Medicine, and supports estimates of a high level of European admixture, accounting for up to half of the genetic make-up of contemporary Ashkenazi.
The genomic analysis also provided information about selection pressures on mutations prevalent in the Ashkenazi Jewish population, such as those leading to conditions like Tay-Sachs disease or mutations in cancer susceptibility genes like BRCA1.
This line of research seeks the answer to the question: why doesn't a harmful mutation simply disappear from the population? A classic example of positive selection is sickle-cell anemia. Two copies of the mutation are required for the disease to occur, but when an individual has one copy of the mutation, it provides resistance against malaria. Some scientists have proposed that disease-related mutations have persisted in the Ashkenazi Jewish population because of a similar hidden positive effect.
"Only six of the 21 disease genes that we examined showed evidence of selection," Bray says. "This supports the argument that most of the Ashkenazi-prevalent diseases are not generally being selected for, but instead are likely a result of a genetic bottleneck effect, followed by random drift."
Besides examining the genes responsible for previously identified diseases, Bray and colleagues went on to look for other regions of the Ashkenazi Jewish genome that display signs of selection, in comparison to European genomes. The two strongest differences between the Ashkenazi and European populations were on chromosome 2 and 12. A region including the lactase gene, which confers lactose tolerance, on chromosome 2 showed signs of strong selection in Europeans but not the Ashkenazi.
"A variant of the lactase gene swept through Europe at around the same time as the domestication of cattle several thousand years ago," Bray says. "This result suggests the selection preceded the European establishment of the Ashkenazi Jewish population, which is consistent with the historical record."
In addition, a region on chromosome 12 showed selection in the Ashkenazi Jewish population but not Europeans. This area encompasses 18 genes but the investigators noticed that one of these, ALDH2, is important in alcohol metabolism, and genetic variation in ALDH2 has previously been shown to affect alcohol consumption, Bray says.
"This is consistent with historical and modern reports of lower alcoholism rates in Jews, although social and religious practices are also thought to play a role," he says. "However, a more detailed analysis of variants in the ALDH2 gene would be necessary to show a mechanistic link."
The research was supported by the National Institutes of Health.
Writer: Quinn Eastman
S.M. Bray, J.G. Mulle, A.F. Dodd, A.E. Pulver, S. Wooding and S.T. Warren. Signatures of founder effects, admixture and selection in the Ashkenazi Jewish population. PNAS Early Edition (2010).
J.G. Mulle, et al. Microdeletions of 3q29 confer high risk for schizophrenia. 87, 229-236. Am. J. Hu. Gen (2010).
The Robert W. Woodruff Health Sciences Center of Emory University is an academic health science and service center focused on missions of teaching, research, health care and public service. Its components include the Emory University School of Medicine, Nell Hodgson Woodruff School of Nursing, and Rollins School of Public Health; Yerkes National Primate Research Center; Winship Cancer Institute of Emory University; and Emory Healthcare, the largest, most comprehensive health system in Georgia. Emory Healthcare includes: The Emory Clinic, Emory-Children's Center, Emory University Hospital, Emory University Hospital Midtown, Wesley Woods Center, and Emory University Orthopaedics & Spine Hospital. The Woodruff Health Sciences Center has a $2.5 billion budget, 17,600 employees, 2,500 full-time and 1,500 affiliated faculty, 4,700 students and trainees, and a $5.7 billion economic impact on metro Atlanta.
Learn more about Emory's health sciences: http://emoryhealthblog.com - @emoryhealthsci (Twitter) - http://emoryhealthsciences.org
In the medieval period, Ashkenazim were the most well-traveled people in the world. It was hardly uncommon for Jewish couples to be comprised of a man and a woman who were born in communities located hundreds of miles away from one another at a time when most Christian Europeans married people who were born in a 20 mile radius of their own birthplace.
I'm not sure why this is being represented as an unexpected find.
Agreed. "The Wandering Jew" became almost a mythological label, they were driven away from towns and cities an a regular basis, laws were passed prohibiting them from participation in long lists of professions, and pogroms were enacted against them by numerous groups
If they now didn't have a spread of genetic diversity as a result, that would be the real surprise.
Although come to think of it, perhaps this article is a refutation of the Jewish insistence of genetic/racial purity?
Wherever Jews lived for more than a few generations they absorbed the DNA of surrounding peoples. The Ethiopians came back to Israel looking like Ethiopians, the Indians looking like others in India, the Yemenites like the Yemenites, the Morrocans like the Morrocans and all those pale faces from Europe looking like the pale faces there. “Racial purity” is a concept of our enemies. Israelis marry Israelis no matter what their origin except perhaps in extreme fringe ultra-Orthodox groups who are out of step with the society in this and every other matter.
I'm not aware of any such claim being made by Jews.
The traditional Jewish claim is that all Jews are matrilineal descendants of Abraham except for the most recent converts.
That has little to do with any post-Enlightenment obsession with "racial purity" and more to do with the perennial notion of rightful inheritance.
Thanks decimon....genetically more diverse than people of European descent, despite previous assumptions that Ashkenazi Jews have been an isolated population. In addition, analyses of disease-related genes of higher prevalence in the Ashkenazi Jewish population indicate that only a minority of traits show signs of positive selection, suggesting that most have arisen through random genetic drift... The researchers were able to estimate that between 35 and 55 percent of the modern Ashkenazi genome comes from European descent... The two strongest differences between the Ashkenazi and European populations were on chromosome 2 and 12.To all -- please ping me to other topics which are appropriate for the GGG list.
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Thought it said gnomes...
Eighty percent of the Jewish immigrants to the US are the Ashkenazi Jews.
Study identifies genetic signatures for 3.5 million
"NEW YORK About 3.5 million of todays Ashkenazi Jews 40 percent of the total Ashkenazi population are descended from just four women, a genetic study indicates."
"Those women apparently lived somewhere in Europe within the last 2,000 years, but not necessarily in the same place or even the same century, said lead author Dr. Doron Behar of the Rambam Medical Center in Haifa, Israel."
I wonder if Emory University got Saudi funding for this study?
The Muslims/Arabs are keen on proving the land of Israel, which they call by its Roman name, Palestine, is Arab—not Jewish.
“Proving” the Jews are European rather than Middle Eastern has been a pet project of them.
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I thought it said “gnomes”. I really need MORE coffee.
. . . . and they were really, really tired.
Jewish gnome now, but if you hold it in your hand it turns into a suitcase.
[misappropriated old punchline alert]
I understood “of,” “and,” and “the.”
So did I. Lol!
Could the fact that the Jewish population was small and dispersed but connected in trade also be a factor? They had to search far for mates, increasing heterozygosity.
So can the Federation and synagogues lay off slamming us for intermarrying, as long as we raise ‘em up fully Jewish?? It’s not like the old timers weren’t always doing the same darn thing!
Also, interesting to see the proof that Jews are less likely to be able to tolerate milk, and less likely to have problems with alcohol. We knew it but now we know why.
Once you convert, you are not a convert. You are a Jew. There is no second class of Judaism; at least there is not supposed to be.
Jews are born with a Jewish soul, or neshama. If someone converts to Judaism, they always had that neshama. Time is not a necessary construct for our Maker.
Therefore it doesn't matter how much "Jewish blood" you supposedly have, genetically. Though as we see by this study, at least half our blood is genetically Jewish too.
Eventually, as their children marry, their descendants will acquire that matrilineal ancestry over time.
I am not suggesting that converts are considered less Jewish - just pointing out that Jews do not picture themselves as a "race", but as a family.
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