African-American DNA

+8 votes

Recently I discovered that I have an African-American DNA cousin.  I accomplished this using GEDmatch with SNP = 300 and cM = 3.  In addition to me, she matches four other Barnes-1145 cousins.  Unlike me, she has had a terrible time producing a paper trail.  I would like to help her and hope others might also.  Her maternal surname is the same as my paternal surname.  Of that line, she only knows the name of her great grandfather.  That fact she gleaned from the 1941 death certificate of her grandfather who was born in 1893.  One more generation and we will overlap the Emancipation Proclamation era.

My and her immigrant’s extended family were Quakers, who did not believe in slavery.  One son of the immigrant bolted rank and owned slaves.  For this reason, we can isolate my cousins ancestor to a very small group of males.  I am identifying these males by name since slaves were considered valuable property and were Willed from parent to child.

I suspect that based on other cousins on this same immigrant that my African-American cousin is in the range of 5C to 5Cx3.  Is it possible using the less distant ancestors and default setting to find 3rd cousins and dramatically shorten the list of direct ancestors.  Any advise from Peter Roberts, or other DNA experts will be greatly appreciated.

WikiTree profile: Brinsley Barnes
in The Tree House by Anonymous Barnes G2G6 Mach 3 (32.4k points)

What an interesting story - ISOGG has some good information regarding African DNA that might be helpful.

2 Answers

+11 votes
Best answer

I wish you shared 7 cM or better with her.  The 3 cM "match" could simply be a software match and not a DNA one.   There is large amount of uncertainty when you get below 7 cM and the autosomal DNA is unphased.  A segment she received from one of her European ancestors could look somewhat like a segment you received from one of your European ancestors. 

I recommend trying to Y-DNA test distant direct paternal line cousins of the suspected ancestor.  Other options are trying to phase your autosomal DNA ,  or finding X chromosome descendants of the suspected ancestor and see if there is any X-DNA matching.  

I'm starting to see that when a lot of various cousins have tested and an assortment of parent/child relationships are confirmed via matching of mtDNA, Y-DNA, X-DNA, and/or auDNA then you confirm ancestry that you would otherwise not have imagined was possible.  For example you may not have any of your distant ancestor's DNA but some of your cousins do and their matching with each other has confirmed a particular branch of your ancestry as accurate.  Then other DNA matching can build on the confirmations already in place.

Citations are critical in order to allow others to verify that the DNA matching is being used correctly.

Sincerely, Peter


by Peter Roberts G2G6 Pilot (482k points)
edited by Peter Roberts

Hey Hugh and Peter - I also addressed this and the citations part in the other post about this...


+4 votes
Hugh does she match other Barnes at greater than SNP = 300 and cM = 3?

Because ordinarily I would reject that as a match worthy of further consideration. Matches with thresholds set this low can be false positives" due to general population allele frequencies and not because you are actually related. Sometime you can see that a 3cM segment matches to a larger segment shared by a few other people if it has 600+ SNPs which is why I ask. But this is a very SNP-poor segment. So even in that case I wouldn't put any weight on in. Sorry I don't mean to be a buzz kill.

There is a closed group that you and she can join called The African Descendant's Genetic Genealogy run by Shannon Christmas. I am very impressed by his work.
by R B G2G6 Mach 3 (39.8k points)
I agree - I wouldn't take a single shared 3 cM segment as evidence of a relationship - particularly when you do not have a paper trail.

Hi Ray,

I disagree with your comment. As I have answered in more detail here: we're talking not about shared 3cM segment as evidence of a relationship.

We're talking about a triangulated group where all DNA cousins of this TG share one ancestral segment (eg. chromosome 12, 105-113 mBp). It's normal that not everyone in this ancestral segment has the same start and end position or all the matching segments have the same length.

Hugh is pointing out that one of the DNA cousins in the group has a 3cM segment with one of other DNA cousin. He hasn't given any explicit information about how long the other DNA cousins matching segments are but my guess is that some of them are larger than this specific one.

No matter what the person in question matches himself and four other DNA cousins on this ancestral segment. That is the only proof needed to show a relationship.

A paper trail on the other is always the ideal but in some case impossible (adoptions and NPE come to my mind). So when you write:

I wouldn't take a single shared 3 cM segment as evidence of a relationship - particularly when you do not have a paper trail.

then it's not true that the missing paper trail is making the relationship invalid. Otherwise adoptees would always have invalid relationships until they finally find a paper trail.

DNA genealogy doesn't work that way, it's the combination and the best of both, DNA and Genealogy: Proving your family tree through triangulation

Andreas -

I'm not sure why you are fixating on my statement about the paper trail, as if I am dismissing the utility of DNA genealogy.  As I stated, I agree with the points that were made by others about being very cautious in taking a 3 cM matching segment as evidence of a shared ancestor - even if there is triangulation.  I'll say it a different way - a 3 cM matching segment in the absence of any other evidence of a relationship is not convincing evidence of a shared ancestor.

This isn't an opinion on your research.  This statement reflects the extensive work that several leading DNA genealogists have done on small segments under 5cM.  These researchers strongly caution against relying on small segment matches as evidence of a shared ancestor.  For example, here is a thoughtful blog post on this from Blaine Bettinger:

He then extends this post with a review of specific examples of instances in which small segment matches appear among close relatives.  Again - upon further study, the vast majority of the small segment matches turned out to be false matches - even among close relatives (much less for distant relatives):

Finally. you mentioned adoptees and small segments.  CeCe Moore is one of the most vocal critics of the use of small segment matches in DNA genealogy.  She is also one of the leading experts in helping adoptees use DNA genealogy to help find their birth parents:

Bottom line - I would be really cautious about relying heavily on small segment triangulation - particularly in the absence of any other evidence of a relationship.

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