I really enjoyed the presentation Paul Woodbury of Legacy Tree Genealogists did about Endogamy last year at the SCGS Jamboree so I am delighted to present this guest post from him on that topic.
Personally I struggle with the endogamy in my mother’s family tree. My jewish grandad was an only child so there are not that many close cousins on his side. However due to endogamy my maternal aunts have hundreds of 2nd-3rd/4th cousin matches. No wonder I spend more time working with the easier Norwegian DNA from my Dad!
Endogamy and DNA By Paul Woodbury
Autosomal DNA testing is a valuable resource for genealogists seeking to overcome recent brick walls in their family history, particularly in instances where traditional historical research is limited or unavailing. At Legacy Tree Genealogists, we frequently use autosomal DNA test results to answer questions regarding adoption, unknown paternity, or ancestors who are difficult to trace. However, there are some factors that can complicate the use of autosomal DNA in tracing ancestors. One of those factors, which is what we will be discussing in the article, is Endogamy.
Endogamy is the custom of marrying only within the limits of a local community, clan, or tribe over the course of many generations. The reasons for this genetic isolation could be cultural or religious (as with Ashkenazi Jews and Low-German Mennonites) or geographic (as with island and tribal populations). Members of endogamous populations may descend from a limited pool of “founder” ancestors who represented the initial genetic makeup of their population. After many generations and hundreds of years of isolation from outside pedigrees, genetic profiles of population members can easily be distinguished from the DNA of outside populations. However, this can also cause pedigree collapse.
Two days of talks in sunny San Diego with headliners Cece Moore and Blaine Bettinger, what a pleasure for the roughly 275 genetic genealogists attending. I always enjoy any talk by either of them but I had to miss a few to go to other talks, so I am really looking forward to the videos. The people who missed the conference will be able to purchase them in a few weeks from the i4gg site.
Cece presenting the keynote
Those of you who overflowed the room for my talk on GEDmatch, thanks! My slides are always available at slides.com/kittycooper – this talk is called GEDmatch Basics. I also have a handout in the downloads section here on my blog.
So what other talks did I enjoy besides Cece and Blaine? Barbara Rae-Venter’s presentation of the Lisa project story had me on the edge of my chair and actually gave me nightmares. I don’t think I have ever had that happen before from a genetic genealogy lecture! Congratulations to all those DNAadoption.com volunteers who helped sort out that case!
Leah Larkin presents endogamy
I loved that Kathy Johnston pointed out the ancestors that you can inherit X from come in a Fibonacci series of numbers for each generation.
But the surprise delight was Leah Larkin’s endogamy presentation. She is the new editor of the Journal of Online Genetic Genealogy (JOGG) at JOGG.info and has endogamy on her Cajun side. This is a very hard topic to explain and to deal with in your genes but she aced this talk and her slides were terrific.
Endogamous populations are much harder to work with in genetic genealogy because you have double and triple 6th cousins who look like 2nd to 3rd cousins when you compare their DNA to yours. Ashkenazim (see my Ashkenazi DNA post), Mennonites (see Tim Jantzen’s project), and Polynesians (See Kalani Mondoy”s project) are a few of these intermarried groups. See the ISOGG wiki for a further discussion of endogamy.
A fellow genetic genealogist, Israel Pickhotz, has written a fascinating book about how he has confirmed and refuted many genealogical connections in his extended Ashkenazi family. He did this by testing every cousin he could. That story is an inspiration to those of us frustrated by using DNA to research our jewish roots. It is as easy to read as it can be, given that genetic genealogy is not easy to understand. Lara, blogging at her blog Lara’s Family Search, wrote an excellent description of the book in her review which is hard to improve upon.
Israel’s blog continues his story: http://allmyforeparents.blogspot.com/
Another DNA expert, Jim Bartlett has just written an interesting blog post investigating the math of endogamy at his segmentology blog. As it is titled part I, I am looking forward to part II.
The problem comes when so many cousins marry each other as you go back up the tree that it gets difficult to calculate the shared DNA. Plus once you get past 3rd cousins, DNA inheritance becomes more and more random anyway.
On my Norwegian side, my Dad has a woman “MB” listed as a 2nd to 3rd cousin who upon investigation was found to be a fifth cousin three times and a sixth another time. She shares 49 cM over 4 segments with my Dad and a whopping 141 cM in 8 segments with my third cousin in Norway. That third cousin is related the same way to MB as we are, but he, like MB, descends from a cousin marriage within this group.
It has been quite surprising to me to see how often 23andme claims Norwegian relatives are more closely related than they in fact turn out to be. This particularly shows up among those descended from the farms around the Stordalsvatnet (a large glacier lake upstream from Etne in Hordaland Norway) such as Skjold, Frette, Tveito, Lussnes, Sande, Hovland, and Håland to name just a few (Click here for a picture towards Frette from google maps). So when last at the library in Salt Lake City, I photographed pages from the Etnesoga farm books for all these ancestral farms in order to discover the many ways these folk intermarried in recorded genealogical time. I have been entering all this data on GENI and ancestry but have yet to discover good ways to display family trees with so many cousin marriages.
So Dad has an expected 3rd to 4th cousin “MB” from Etne who shares 4 good sized segments and .66% of her DNA with him. She is in fact twice a 4th cousin once removed and once a 6th cousin to him (so far). Most delightful however is that she has four generations of family tested. So here is a picture made with my segment mapper tool of her versus her daughter (.55%), two grandsons (.52% and .38%), a great granddaughter (.39%) and a great grandson (.26%). Clicking on the picture will take you to a copy of the actual output with mouse-over popups showing the centimorgan (cM) values.
As expected, her daughter is a solid blue line as she has half of all her DNA, thus one of every chromosome pair, from her mother. Looking at the two sons, you can see that they inherit some of the same DNA and some different. Notice how all of chromosome 21 has been passed intact all the way to her g-granddaughter. This is the smallest chromosome. The X inheritance is also of interest as MB’s daughter gave each son only one piece from her mother, and not the same pieces. This fits with what I have seen with sluggish recombination on the X