Wednesday, March 29, 2017

Endogamy in Practice: Updated

Almost exactly a year ago, I wrote about how endogamy makes my known relatives share a lot more DNA with me than would be expected--and showed how much DNA they actually share, to help those with endogamous ancestry understand their own matches better.

It is more difficult (but not impossible!) to use genetic genealogy to find relatives when you are from an endogamous background, and how Ashkenazi Jews (AJs) are a typical example.  AJs married within the small pool of AJs for centuries, so we are all related to one another in multiple ways.  I see many people, adoptees in particular, using ISOGG's table with average amounts of shared autosomal DNA for various relationships to determine a match's actual connection.  While that table is a great help for the general population, if you're descended from an endogamous group, the relationships are generally vastly overstated.

Now that I've had even more cousins (with known relationships) test, I figured it was time for an update to give additional insight into how endogamy impacts shared DNA between relatives.  (And if you're a relative of mine who hasn't tested, please do--and you'll likely be featured in some upcoming follow-up!)
Some of my known relatives who have tested, displayed in FamilyTreeDNA

The following shows relatives who have tested and how much DNA each shares with me.

Name Actual Relationship FTDNA's Predicted Relationship Range Shared cM ISOGG average % above avg Comments
Paternal Grandmother Grandmother Half Siblings, Grandparent/ Grandchild, Aunt/ Uncle, Niece/ Nephew 1327.1794 1700 -22%
Paternal uncle Uncle Full Siblings, Half Siblings, Grandparent/ Grandchild, Aunt/ Uncle, Niece/ Nephew 1955.2031 1700 15%
Paternal aunt Aunt Full Siblings, Half Siblings, Grandparent/ Grandchild, Aunt/ Uncle, Niece/ Nephew 2197.4289 1700 29.3%
Maternal uncle Uncle Half Siblings, Grandparent/ Grandchild, Aunt/ Uncle , Niece/ Nephew 1848.0041 1700 8.7%
Ruth Great Aunt 1st Cousin, Half Siblings, Grandparent/ Grandchild, Aunt/ Uncle, Niece/ Nephew 1008.4038 850 18.6%
Scott 1C1R 1st Cousin, Aunt/ Uncle, Niece/ Nephew 685.0191 425 61%
Karen 1C1R 1st Cousin - 2nd Cousin 460.8610 425 8.4%
George 1C2R 1st Cousin - 3rd Cousin
212.5 45.1%
Mitzi 1C2R 1st Cousin - 3rd Cousin
212.5 66.4%
(George & Mitzi's 1/2 1C)
Half 1C2R 2nd Cousin - 3rd Cousin 206.0462 106.25 93.9%
2C1R 2nd Cousin - 3rd Cousin 195.8675 106.25 84.3%
Sandy (Leslie's 2C) 2C1R 2nd Cousin - 3rd Cousin 163.7570 106.25 54.1%
Mark (Leslie & Sandy's 2C1R) 3C 2nd Cousin - 3rd Cousin 179.2561 53.13 237.3% 3/4 AJ
Benjamin 2C2R 2nd Cousin - 3rd Cousin 170.4922 53.13 220.9%
Ken 2C2R 2nd Cousin - 3rd Cousin 108.1761 53.13 103%
(2nd cousin to Ken & Marilyn; 1/2 second cousin to Sue)
2C2R 3rd Cousin - 5th Cousin 174.8590 53.13 229.1%
(2nd cousin to Ken & Myron; 1/2 second cousin to Sue)
2C2R 3.8 generations (GedMatch) 70.7 53.13 33.1%
(Myron's niece)
3C1R 3rd Cousin - 5th Cousin 89.1355 26.56 235%
(1/2 second cousin to Ken, Marilyn & Myron)
Half 2C2R 2nd Cousin - 4th Cousin 103.5133 26.56 289%
JudithK 2C1R 2nd Cousin - 3rd Cousin 205.8208 106.25 93.7%
Leon (1C to JudithK & Jerry) 2C1R 2nd Cousin - 3rd Cousin 163.2738 106.25 53.7%
Jerry (1C to JudithK & Leon) 2C1R 2nd Cousin - 3rd Cousin 248.6424 106.25 134%
Fern (2C to JudithK, Leon & Jerry) 2C1R 2nd Cousin - 3rd Cousin 231.9087 106.25 118.2%
Beth 2C1R 2nd Cousin - 3rd Cousin 232.1945 106.25 118.5% 2 AJ grandparents
(Beth's nephew)
3C 1st Cousin - 3rd Cousin 276.0552 53.13 419.6% 1 AJ grandparent
(Beth's niece, Dave's 1C)
3C 2nd Cousin - 4th Cousin 110.1238 53.13 107.2% 1 AJ grandparent
Elise 3C1R 3.3 Generations (GedMatch) 142.4 26.56 436.1%
Ron 3C1R 2nd Cousin - 4th Cousin 100.8463 26.56 73.7%
Esther 3C1R, 3C1R 3.2 Generations (GedMatch) 166.6 26.56x2
213.6 Grandparents were Eizikovic first cousins
JudithB (Esther's sister) 3C1R, 3C1R 2nd Cousin - 3rd Cousin 186.3940 26.56x2
250.9% Grandparents were Eizikovic first cousins
Jonathan (JudithB's son, Esther's nephew) 4C 2nd Cousin - 3rd Cousin 182.0750 13.28x2
585.5% Great-grandparents were Eizikovic first cousins
Pat 2C1R 2nd Cousin - 4th Cousin 117.5067 106.25 10.6%
Ben 3C, 4C 3rd Cousin - 5th Cousin 101.6712 53.13 + 13.28 =
53% Has 2 Supkoff great grandparents
Table Showing Actual & Genetic Relationships Between Myself and Known Relatives

In the above chart, the columns represent the following:
  1. The first column is the relative who has tested
  2. The second column is the testee's known relationship to me; xCyR means that the person is an xth cousin, y times removed.
  3. The third column is FamilyTreeDNA's predicted relationship range between myself and the relative.  Note that FTDNA does try to adjust this somewhat for those with Jewish DNA.  If the person has not tested at FTDNA, I use GedMatch's estimate.
  4. The fourth columns is how many cM of DNA I share with the individual
  5. The fifth column is how much I'd be expected to share with that individual, per ISOGG's Autosomal DNA statistics.
  6. The sixth column is the percentage of cM shared above what would be expected for a specific relationship.
  7. Finally, the seventh column has additional information about the individual which may be relevant.
Unless specifically noted, all of the individuals on this list had 4 Ashkenazi Jewish (AJ) grandparents.

With the exception of my grandmother (I guess I got more DNA from my paternal grandfather than grandmother), every single individual on this list shares significantly more cM with me than would be expected for their known level of cousinship.  Even Dave, who has only 1 Jewish grandparent, shares more than four times the expected amount of DNA with me.

Hopefully this will give more insight into what different values for shared cMs can really mean when dealing with Ashkenazi ancestry.  And good luck.  You'll need it.

Note:  I'm on Twitter.  Feel free to follow me (@larasgenealogy).

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  1. I only have two confirmed relationships I can compare with your numbers. My uncle is 1861.27 cM (+9.5%), my 3rd cousin is 107.487 (+102.3%) and my uncle to my 3rd cousin (i.e. 2nd cousin, once removed) is 134.789 (+26.9%).

  2. So two comments if I may:

    Is this saying that for Ashkenazi Jews, (89% in my case) the relationships listed in FTDNA are probably overstated? That is, if it says 2nd-3rd cousin, that's probably too high? The numbers I am seeing seem to bear that out.

    Second, in your experience, is there a geographical area that has more difficulty for Jews to discover family connections than others? I am 61, much of my family in Hungary was exterminated in the Holocaust. As well, pretty good chance that the parents of my cousins would probably have passed by now. Thank you

    1. Your first comment is generally true. Look at largest segment to try to find the true matches; see my post here:

      For the second, you'd be surprised. I've found cousins on my Hungarian side via DNA--including 6th cousin. I also discovered that my grandfather's aunt (on my then-Poland, now-Ukraine side) wasn't killed in the Holocaust like we thought, as I got a good match with her great grandson (Dave who's mentioned in this post).

  3. As someone who is about 50 percent Jewish, any idea how this should look?

    1. Good question. Well, you can see a bit with my relatives who have some non-Jewish ancestry. But I should do another blog post looking at those relatives in comparison to their known Jewish relatives who have tested. It will be a month or so because there are 2 tests processing that will be very informative for that.

  4. This is also the same for Maltese ancestry

  5. Good to see a blog post comparing these. In your FTDNA totals did you use the total shown in the Matches list or did you view in Chromosome Browser and only count the segments which were 7 cMs or greater for your comparison totals? This is something I always recommend to anyone using FTDNA to get an idea of possible relationships, I don't have any Jewish lines but I do have mostly Colonial American on both sides so I see this on a somewhat smaller scale.

    1. I used FTDNA's totals, since that's what people mostly look at when trying to determine relationships. (And with AJ DNA, 7cM segments aren't very informative in general either)--you want to go at least double--or triple--that number.

  6. Interesting study.
    It's interesting how many of them fall within the Shared cM Chart's range, even with the inclusion of all of FTDNAs short segments.

    At least til you get down to the 4th cousins. Of course, knowing who is a 4th cousin to know they are "off the chart" is a challenge in and of itself. I'm trying to find an unknown AJ father. Not much other info than that he was in a certain location at a certain time (to have conceived the child.) No match closer than about a 2C1R so far (which might well be further than he looks, of coure, and he is an adoptee, so is of minimal help.) Keep hoping for new matches!
    Thank you for sharing!

  7. In AJ- what is more important in determining how close someone is- total cM or longest cM? For example- one with total 160 and longest 14 or somebody with total 76 longest 28?

    1. The second of the two. But it's really an interplay between the two numbers.