Y-chromosomal Aaron
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[edit] Background
Although membership in the Jewish community is traditionally passed maternally (see: Who is a Jew), membership in the group that originally comprised the Jewish priesthood ("Kohens" or Kohanim), is patrilineal, and modern Kohens claim descent from Aaron, brother of Moses.
In genetics, it is understood that the normal number of chromosomes is 46, of which 23 are inherited from each parent. Two chromosomes, the X chromosome and Y chromosome, determine gender. Women have two X chromosomes, one inherited from their mother, and one inherited from their father. Men have an X chromosome inherited from their mother, and a Y chromosome inherited from their father.
Males who share a common patrilineal ancestor should also share a Y chromosome, diverging only with respect to accumulated mutations. Since male children get their Y chromosome from their father, all Kohanim should theoretically share the same Y chromosome, apart from any genetic mutations that may have occurred since the time of Aaron. Mutations on the Y chromosome occur at a relatively constant rate, allowing scientists to estimate the time that has passed since carriers of similar Y chromosomes had a common ancestor. (See molecular clock.)
(Another kind of DNA, Mitochondrial DNA (mtDNA), is not on any chromosome, but is instead passed from mother to child in the mitochondria of the egg. This almost always comes only from the mother, and also remains unchanged except for accumulated mutations.)
[edit] The hypothesis
This hypothesis was first tested by Prof. Karl Skorecki and collaborators from Haifa, Israel, in 1997. In their study, "Y chromosomes of Jewish priests," published in the journal Nature, they noted that in fact many Kohanim share certain Y-chromosome markers. Other studies (Thomas MG et al, 1998) have corroborated the findings, and have dated the origin of the shared DNA to approximately 3,000 years ago (with variance arising from different generation lengths). The techniques used to find Y-chromosomal Aaron were first popularized in relation to the search for the patrilineal ancestor of all contemporary living humans, Y-chromosomal Adam.
[edit] Structure of the Cohen Modal Haplotype
The Cohen Modal Haplotype, which can be identified with a genealogical DNA test, is:
DYS19/DYS394 = 14 DYS385a = 13 DYS385b =15 DYS388 = 16 DYS389-1 = 13 DYS389-2 = 30 DYS390 = 23 DYS391 = 10 DYS392 = 11 DYS393 = 12 DYS426 = 11 DYS439 = 12
The Cohen Modal Haplotype belongs to haplogroup J.
The 12 marker Cohen Modal Haplotype (CMH-12) is based upon studies by a private company. It has not been peer group reviewed by other scientists or published in the open technical literature. It is the 6 marker Cohen Modal Haplotype (CMH-6)that is the basis for current technical publications. These markers (CMH-6) are given by:
DYS19 = 14 DYS388 = 16 DYS390 = 23 DYS391 = 10 DYS392 = 11 DYS393 = 12
[edit] Criticism and response
Understandably, the finding led to a lot of excitement in religious circles, providing some "proof" of the historical veracity of the Bible<ref>[1] [2]</ref>, but also leading to criticism<ref>[3]</ref>.
[edit] Other carriers of the DNA
Critics of the theory point out that the Cohen Modal Haplotype has also been found in significant numbers in groups of non-Jews, notably Italians. However proponents of the theory are quick to explain these anomalies. They state that history records the migration of large numbers of Jewish slaves to Rome (what is now Italy), particularly in association with the building of the Colosseum.
However, the Cohen Haplotype has also been found among significant numbers of non-Jewish Arab and Kurdish populations. Although this too could be explained in part by miscegenation, assimilation, and conversions, there is an alternate possibility that the marker precedes all of these populations and is a precursor to some common ancestral group.
[edit] Lemba
The Cohen Modal Haplotype has also been found in the Lemba of Southern Africa, who have a tradition of Jewish ancestry<ref>Thomas MG et al 2000</ref>.
[edit] Kurds
The Cohen Modal Haplotype has also been found in some groups of Kurds. There are a number of Kurdish Jews.
[edit] Founder effect
People who do not believe in the validity of the Cohen Modal Haplotype say that such efforts to detect a genetic signature's survival in the Y chromosome unchanged over 3,500 years (approximately the amount of time since the time of the patriarchs) seem misplaced. While it has been shown that surname studies and Y-DNA matches validate each other<ref>for instance in a 2006 study of Germans by Uta-Dorothee Immel’s team of population geneticists</ref>, the most current research increasingly points to a relatively recent historical timeframe for founder effects and matching haplotypes.
According to a study by a forensic team<ref>the forensic team of Heyer et al. in 1997</ref>, the average mutation rate for Y-STRs (the "alleles" that create differences in haplotype scores) is 2.1 x 10(-3), or once every 476 generations, i.e., once every 14,280 years. But this estimate is computed on the basis of one allele changing – on its either increasing by 1 or its diminishing by 1. Where most people err is to forget that these statistics apply to one marker. For the six markers, the approximate 50% point for one mutation would be one-sixth or 2400 years.
Hence, even if Aaron's progeny did prosper and survive over the millennia, they would have split into dozens of different genealogies. Some believe that if the discoverers of the "Cohen Modal Haplotype"<ref>Skorecki, Thomas, Hammer and company</ref> found any modal Jewish haplotype at all it is probably the genes of a prolific medieval rabbi who lived about 1000 years ago and had numerous sons and grandsons. Others argue that the fact that so many people with a family belief of being Cohanim have tested positive for the Cohen Modal Haplotype offers proof of its validity. The former conclusion consorts better with the emerging consensus that the roots of the human family tree are much shallower than previously believed. However, mutation rates are bitterly disputed and only longitudinal studies such as comparisons available to large DNA projects will yield secure estimates. [Surname projects are limited to recent western Christian populations and do not apply to other cultural groups.]
[edit] Y-chromosomal Levi?
While Kohanim are believed to have descended in the patrilineal line from Aaron, brother of Moses, Levites (a second level of Jewish priesthood) are traditionally believed to have descended in the patrilineal line from Levi, son of Jacob. Levites should also therefore share common Y-chromosomal DNA.
An investigation of men who consider themselves Levites found high frequencies of multiple distinct markers, suggestive of multiple origins for the majority of non-Aaronid Levite families. One marker, however, present in more than 50% of Eastern European (Ashkenazi) Jewish Levites points to a common male ancestor or very few male ancestors within the last 2000 years for many Levites of the Ashkenazi community. The hypothetical ancestor most likely lived at the time of the Ashkenazi settlement in Eastern Europe.<ref>http://www.ucl.ac.uk/tcga/tcgapdf/Behar-AJHG-03.pdf</ref>
[edit] See also
[edit] References
<references />
- Skorecki K, Selig S, Blazer S, Bradman R, Bradman N, Waburton PJ, Ismajlowicz M, Hammer MF. Y chromosomes of Jewish priests. Nature 1997;385:32. PMID 8985243.
- Thomas MG, Skorecki K, Ben-Ami H, Parfitt T, Bradman N, Goldstein DB. Origins of Old Testament priests. Nature 1998;394:138-40. PMID 9671297.
- Thomas MG, Parfitt T, Weiss DA, Skorecki K, Wilson JF, le Roux M, Bradman N, Goldstein DB. Y chromosomes traveling south: the Cohen modal haplotype and the origins of the Lemba--the "Black Jews of Southern Africa". Am J Hum Genet 2000;66:674-86. PMID 10677325.
[edit] External links
- A summary of Jewish & Kohanim genetic research papers
- Origin, Diffusion, and Differentiation of Y-Chromosome Haplogroups E and J: Inferences on the Neolithization of Europe and Later Migratory Events in the Mediterranean Area
- The Y chromosome pool of Jews as part of the genetic landscape of the Middle East by Nebel et al.de:Aaron des Y-Chromosoms
