Partially Endogamous DNA

I've written a lot about my 100% Ashkenazi Jewish (AJ) heritage and how that means I share way more DNA with known cousins than would be expected.  But what about people who have some AJ heritage but also have ancestors with other backgrounds?  Do they still need to account for endogamy?  To see how partial endogamy impacts amounts of shared DNA with relatives on the endogamous side, I looked at relatives who have tested who are partially AJ (including those that are 3/4, 1/2, 1/4 and 1/8 AJ) to see how endogamy impacts DNA they share with others.

Analysis of shared DNA for those with partial Ashkenazic Jewish ancestry (in blue) with known relatives (details below)

Mark (3/4 AJ)

My third cousin Mark is 3/4 Jewish; all of his grandparents were Jewish with the exception of his maternal grandfather.  The following demonstrates how much DNA he shares with known relatives, as opposed to how much he'd be expected to share.

Name	Actual Relationship	Shared cM	ISOGG average	% above avg	Comments
Eddie	2C1R	184.8	106.25	73.9%
Linda	2C1R	189.3	106.25	78.1%
Karen	2C1R	101.0	106.25	-4.9%
Leslie	2C1R	140.7	106.25	32.4%
Sandy	2C1R	165.4	106.25	55%	3/4 AJ
Ken	2C2R	180.7	53.13	240%
Marilyn	2C2R	162.0	53.13	201.1%
Myron	2C2R	93.7	53.13	76.4%
Sue	1/2 2C2R	21.7	26.56	-8.4%
Me	3C	108.8	53.13	104.8%
Sara	3C1R	75.9	26.56	185.8%

Unlike my own 100% AJ results, Mark's results are a bit more mixed.  He does have several matches that share significantly more DNA with him than would be expected--up to 240% in the case of his second cousin, twice removed Ken.  But there are a few cousins who share just a bit less than would be expected.

Sandy (3/4 AJ)

Sandy is my second cousin once removed.  Her grandparents are Jewish with the exception of her paternal grandfather.

Name	Actual Relationship	Shared cM	ISOGG average	% above avg	Comments
Eddie	2C	169.1	212.5	-20.4%
Linda	2C	324.2	212.5	52.6%
Karen	2C	174.9	212.5	-21.5%
Leslie	2C	244.1	212.5	14.8%
Mark	2C1R	165.4	106.25	55.7%	3/4 AJ
Ken	2C1R	128.4	106.25	20.8%
Marilyn	2C1R	171.6	106.25	61.5%
Myron	2C1R	125.9	106.25	18.5%
Me	2C1R	131.9	106.25	24.1%
Sue	1/2 2C1R	89.1	53.13	68.5%
Sara	3C	71.8	53.13	35.1%

Sandy's results are even more mixed than Mark's.  Interestingly, while Sandy and my mother Linda share 52.6% more DNA than would be expected with their relationship, Sandy shares 20.4% less DNA with my uncle Eddie (Linda's brother) than expected.

Beth, Liz, Dave & Shannon (in blue) are partially Ashkenazi.  Below, their shared DNA with the yellow individuals is analyzed.

Beth (1/2 AJ)

Beth is my first cousin once removed.  Her mother was Jewish; her father was not, so her DNA is 50% Jewish.

Name	Actual Relationship	Shared cM	ISOGG average	% above avg	Comments
Marvin	2C	334.7	212.5	57.5%
Sid	2C	337.0	212.5	58.5%
Susie	2C	363.5	212.5	71.1%
Berly	2C	183.3	212.5	-13.7%
Paula	2C	218.2	212.5	2.6%
Me	2C1R	214.0	106.25	101.4%

Beth shares more DNA than expected with my father (Marvin) and his siblings Sid and Susie.  But she shares close to the expected value with their first cousins Berly and Paula.  Perhaps this is because my grandmother shares quite a bit of DNA (in multiple small segments) with Beth--but maybe Paula & Berly's father didn't.  And I inherited much of the DNA which my father shared with Beth.

Dave (1/4 AJ)

Beth's nephew Dave had one Jewish grandparent paternal grandmother, so he has 1/4 Jewish DNA.

Name	Actual Relationship	Shared cM	ISOGG average	% above avg	Comments
Marvin	2C1R	397.7	106.25	274.3%
Sid	2C1R	263.4	106.25	148.0%
Susie	2C1R	409.5	106.25	285.4%
Berly	2C1R	73.6	106.25	-30.7%
Paula	2C1R	63.1	106.25	-40.6%
Me	3C	300.7	53.13	466.0%

Here too, there are significantly larger amounts of shared DNA between Dave and my father and his siblings than between Dave and my father's first cousins.  And I share significantly more DNA with Dave than would be expected with a third cousin.

Liz (1/4 AJ)

Liz is a niece of Beth and a first cousin of Dave.  Her only Jewish grandparent was her maternal grandmother, so 25% of her DNA is endogamous.

Name	Actual Relationship	Shared cM	ISOGG average	% above avg	Comments
Marvin	2C1R	167.6	106.25	57.7%
Sid	2C1R	145.7	106.25	37.1%
Susie	2C1R	265.2	106.25	149.6%
Berly	2C1R	134.8	106.25	26.9%
Paula	2C1R	169.4	106.25	59.4%
Me	3C	103.6	53.13	95.0%

Even though Liz has the same relationship to my branch of the family as her first cousin Dave, the amounts of DNA she shares with my father, his siblings, and his first cousins, are more stable than Dave (although Susie is somewhat of an outlier).  However, note that all of these matches are above what would be expected given the known relationships.

Shannon (1/8 AJ)

Liz's daughter Shannon has only one Jewish great grandparent (up her direct maternal line), so only about 1/8 of her DNA is endogamous.

Name	Actual Relationship	Shared cM	ISOGG average	% above avg	Comments
Marvin	2C2R	117.1	53.13	120.4%
Sid	2C2R	89.6	53.13	68.6%
Susie	2C2R	143.0	53.13	169.1%
Berly	2C2R	69	53.13	29.9%
Paula	2C2R	76.9	53.13	44.7%
Me	3C1R	72.3	26.56	172.2%

Even though Shannon is only 1/8 AJ, endogamy still seems to be impacting how much DNA she shares with known relatives.  All 6 of her known relatives who have tested share more DNA with her than expected--sometimes quite a bit more.

So what conclusions can be drawn here?  Unfortunately things aren't as clear-cut as when one is dealing with 100% AJ DNA.  In some instances, the amount of shared DNA between an individual with partial AJ DNA and a known relative with full AJ DNA is actually quite close to the expected value.  But there are multiple examples--even when the AJ ancestor was several generations back--where a partially endogamous individual shares significantly more DNA with a relative than would be expected.

So if you have partial AJ ancestry, realize that large amounts of DNA may actually be due to endogamy--but not always.  Keep an open mind.

Note:  I'm on Twitter.  Follow me (@larasgenealogy).

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