Going Deeper

What Next?

You've been learning about genetic genealogy, and perhaps have found a few new distant cousins or at least possible cousins. Where might you go from here? Can you also use your DNA test results in new ways? There are many directions you can follow, depending on your personal interests. On this page you'll find links to topics and resources that might intrigue you.

Contents

  • Intermediate Genetic Genealogy Topics
    • Jewish Genetic Genealogy
    • Surname and Location Projects
    • Y-chromosome DNA Testing
    • Mitochondrial DNA Testing
    • Admixture & Ethnicity
    • Genetic Diseases & Trait Analysis
  • Advanced Genetic Genealogy Topics
    • DNA Segment Analysis
    • Genetic Anthropology
    • Genome-wide Association Studies

Intermediate Genetic Genealogy Topics

Jewish Genetic Genealogy

Jewish genetic genealogy is like other genetic genealogy but with a few additions and complications. The main complication is "endogamy," which is the cultural custom of marrying within a group. The genetic genealogical consequence is that there is a higher baseline amount of DNA in common between Jewish people than among a random group, and this appears very strongly in the Ashkenazi Jewish population.

DNA matching to find relatives is based on the amount of shared DNA. The practical result of endogamy for Jewish genetic genealogy is that most of the people that DNA testing typically suggests (based solely on the amount of DNA in common) are 3rd cousins are usually 4th-6th cousins. Even many or most predicted 2nd cousins are actually 3rd-5th cousins.

Because of endogamy, additional information is very important for screening matches to identify closer relatives. This can include finding shared surnames, geographical matching of ancestral birthplaces, comparing family trees, traditional genealogical documentation, and considering the size of individual matching DNA segments rather than just their combined total length.



Surname and Location Projects

... To be added....


Y-chromosome DNA Testing

The human Y-chromosome (Ychr) is only found in males, who receive it from their father. Therefore, it serves as a genetic marker for the patrilineal (direct paternal) lineage. Because the Y-chromosome is preserved intact with each generation, in contrast to other chromosomes, it can be used to trace lineages back hundreds, thousands, and even tens of thousands of years. Population migration studies based on modern and ancient DNA show that most Jewish men have Y-chromosomes that come from the Middle East.

A particularly interesting situation arises around the Kohanim priesthood tradition in Judaism, which is passed down paternally and is traditionally said to derive from Moses's brother Aaron as told in the Torah. If the only source of new Kohanim were patrilineal descendants of one historical man, then all modern Kohanim would share the same Y-chromosome. They do not, but there are a few Y-chromosome "clans" that are particularly common among today's Kohanim. This suggests that a small number of men in ancient times formed the original Kohanim, but there may have been a few new "adopted" lineages added since then.



Mitochondrial DNA Testing

Mitochondrial DNA (mtDNA) is found in both males and females, but children only inherit mitochondrial DNA from their mother. Therefore, mtDNA serves as a genetic marker for the matrilineal (direct maternal) lineage. Like the Y-chromosome (Ychr), mtDNA is preserved intact across generation, and therefore can be used for deep ancestry studies. However, it mutates much more rarely than the Ychr, and therefore has limited use within a genealogical timeframe (the most recent 500 years).

Population studies have shown that most mtDNA of modern Ashkenazim originated from Europe and not the Middle East around and before the time the Ashkenazi population was founded roughly 700 years ago. Given that the Ychr of most Ashkenazi men comes from the Middle East, we can conclude that the Ashkenazi population was mostly founded by Jewish men who migrated from the Middle East and married native European women. Some modern Ashkenazim do carry mtDNA with a Middle Eastern origin, so there were some Middle Eastern Jews who immigrated to Europe as families around or before the time of the Ashkenazi founding.



Admixture & Ethnicity

Is there such a thing as Jewish DNA? Sort of. Does having "Jewish DNA" make you Jewish? Nope. What does "Jewish" mean in a genetic genealogy ethnicity report anyway? It's complicated.

It is conceptually useful to separate the religion of Judaism from the ancient and modern tribal population of the Hebrew people. Jewish religious identity has absolutely nothing to do with DNA—nothing about your DNA makes you a Jew or not.

Genetic identification as a member of the Hebrew tribe in general is complicated by the influx of non-Hebrews through conversion and marriage during the past several thousand years. However, the endogamy and historically low intermarriage rate of Ashkenazim in particular has resulted in a well-defined set of genetic markers that reliably identify members of this specific population and their recently intermarried descendants.

Although Ashkenazi DNA can be reliably identified when present in at least moderate amounts (>5%), Sephardi, Mizrahi, Ethiopian and other segments of the world Jewish population are more challenging. Only some DNA testing companies currently attempt to distinguish those other sources of DNA, but more may in the future as the number of tested members from each sub-population grows.



Genetic Diseases & Trait Analysis

There is a common misconception that Ashkenazi Jews have a much higher frequency of genetic disorders than other populations. This is not true. The misconception arose mostly because the Ashkenazi community has frequently been selected for biomedical research studies because it is well-defined genetically, is a fairly large population, shows a few diseases that serve as useful models for genetic disease in general, and is culturally amenable to scientific research.

Like all well-defined genetic populations, Ashkenazim carry some heritable diseases whose causative genes are more common than in other populations. But there are other genetic diseases that are less common. In addition, the highly publicized program to identify carriers of Tay-Sachs disease resulted in plummeting numbers of new Tay-Sachs cases, and may lead to the near elimination of this disease from the Ashkenazi population within a few more generations. Other genetic diseases of Ashkenazim may similarly follow.


Advanced Genetic Genealogy Topics

Sections to be added...

  • DNA Segment Analysis
  • Genetic Anthropology
  • Genome-wide Association Studies

DNA Special Interest Group