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Amongst the descendants of one of my 2nd great grandmothers there is a strong family legend that her first child was conceived in the 1850s by a man other than the husband she married soon afterwards, and with whom she went on to have multiple other children.

I have recently had my autosomal DNA tested with AncestryDNA and can see that I fall into DNA Circles, for both my 2nd great grandmother and her husband (my 2nd great grandfather), with a number of descendants of three of those multiple other children, which is what I would expect.

The other 8 members of my 2nd great grandmother's DNA circle are:

  • 5 x 3rd cousins averaging 30.38 centimorgans (range 8.9-54) across 3.2 DNA segments (range 2-4) shared with me
  • 3 x 3rd cousins once removed - all 0 centimorgans across 0 DNA segments shared with me

So far no descendants of my 2nd great grandmother's first born have shown up in either of these DNA Circles, which I suspect may indicate that none of them have tested.

At this stage I am not planning to ask them if they might be interested in testing, but what I am interested to know is whether, if they decide themselves to test, whether their appearance in the DNA Circle of my 2nd great grandmother and absence from the DNA Circle of my 2nd great grandfather would add credence to the family legend of the first child's conception.

The suspected father of this first child was prominent, and a later step may be to investigate whether any descendants of the first born fall into the DNA Circle (if one emerges) for that man.

I have not seen the birth certificate of this first child but have no reason to suspect that it would shed any light because I believe it will name my 2nd great grandfather as being the father.

Can Ancestry DNA Circles be useful for distinguishing fathers of children to a 2nd great grandmother?

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I think the answer is probably "it depends" -- and it may not be possible to do this with the information displayed for an AncestryDNA circle alone.

You may find the following resources helpful:

From the DNA Circles White Paper:

One pertinent point relating to IBD [identity-by-descent] is that even if two AncestryDNA members are both descended from a particular ancestor, they may not necessarily share any DNA inherited IBD (e.g., individuals C and E in Figure 2.1). Due to the randomness of genetic inheritance, one doesn't necessarily share DNA with all of one's distant cousins, particularly fourth cousins and beyond. While sharing DNA identical-by-descent is often evidence of the relatedness of two individuals, the lack of an IBD match does not necessarily imply a lack of a distant genealogical relationship.

Thus, the third and final goal of DNA Circles is to allow relatives who do not share identical-by-descent stretches of DNA to collaborate with one another.

The white paper also discusses the problem that a user of AncestryDNA may not have a completely-filled out pedigree, that the pedigree may not be accurate, and that the users who have been grouped together in a DNA Circle may actually have an IBD match because of a different most recent common ancestor (MCRA) than the Ancestor shown in the circle.

The size of the DNA Circle and the confidence scores of the matches for the members are taken into account, and the Whitepaper addresses how these factors affect Ancestry's algorithms.

The white paper on DNA Matching yields another important clue:

An important feature of our method is that we do not keep track of all matching segments; in step 5, we filter out a candidate match if its genetic distance is less than 6cM.

You may be able to infer more than Ancestry's DNA Circle displays tell you, if any of the members of the Circle have also uploaded their data to GEDMatch or you have other means to view their results on a site with a chromosome browser.

Roberta Estes's post Shared cM Project 2017 Update Combined Chart updates the information in Concepts – Relationship Predictions -- comparing the expected percentages and shared cM for certain relationships with what values are being reported to the project.

I think it's definitely a question worth asking, but whether the answer is YES or NO may depend entirely on the specific DNA Circle -- how many people are in the circle, how complete and accurate their paper-trail research is, and how distant the members' relationships are to you.

These recent posts by Blaine Bettinger discuss the problem of small segment matches and may also be of interest:

See especially this caution:

EDIT (4 December 2014) – Ann Turner has noted that the genomes used to generate the graph above were phased using the popular BEAGLE phasing program. The segment data we get from 23andMe and Family Tree DNA, on the other hand, is based on unphased genomes.

Further caution (added October 2018) -- apparently DNA Circles may not be formed if the trees with the same people have small variations in a person's name. If one tree lists a middle initial and the other doesn't, for example, the algorithm won't match them.

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    @PolyGeo I would encourage you to seek out publications by African-American researchers on combining DNA with their paper-trail research. They may be more used to working with very distant relationships. Seeing their worked case studies may give you a baseline for what is possible. – Jan Murphy Sep 1 '17 at 3:52
  • Are there some missing links in your first bullet list? – Ellen Spertus Oct 23 '18 at 19:33
  • Thanks @EllenSpertus I'll fix that. – Jan Murphy Oct 23 '18 at 19:35

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