Walking the Ancestor Back

A segment-ology TIDBIT

Here is an example of walking the ancestor back. I just extended one more generation today, giving four intermediate cousins all in the same line of descent from the CA.

The TG is [14B24] 18-30Mbp about 18cM – [14B24] indicates Chr 14, start in 10-20Mbp area, ahnentafel to CA starts 2-4 – some show this as PP]

The following line of descent is all in VA/WV [the four CAs are bolded]:

Common Ancestor: Sylvester WELCH 1696-1753; 1m 1720 Anne SPENCE: Match KBD at ADNA for 9.9cM is 6C1R

MRCA is son: Sylvester WELCH 1729-1810; m c1752 Jemima CARROLL; Match PDJ at FTDNA for 10.1cM is 5C

Dau: Elizabeth WELCH 1777-1847; m 1797 James FLEMING

MRCA is dau: Sarah FLEMING 1809-1854; m 1827 John H BARTLETT: Match LWA at FTDNA for 16.2cM is 3C

MRCA is son: James V BARTLETT 1836-1920; 1m Elizabeth J NEWLON: Match CK at 23andMe for 54.1cM is 2C1R [this segment overlaps the next TG, too]


Son: James V BARTLETT m Betty V BAKER

Son: jvb jr = me!


A Segment-ology TIDBIT

[22F] Segment-ology: Walking the Ancestor Back TIDBIT by Jim Bartlett 20170103

13 thoughts on “Walking the Ancestor Back

  1. Pingback: Triangulating Your Genome | segment-ology

  2. Jim, You and I are related via your WELCH line. I descend from the following:

    Major John Welsh (d. 1684),
    Col. John Welsh II (brother to your Sylvester Welch. b.c. 1670),
    Capt. John Welsh III,
    Samuel Welsh,
    Warner Welsh,
    Luther Brooke Welsh,
    Luther, Welsh, Jr.,
    Major John Hanna Welsh
    Luther Welsh (1924-1991)
    James Hanna Welsh (me)

    I have done autosomal DNA testing with Ancestry and Y-DNA with FTDNA (Kit # 653361). At one time you were looking for living male-line relations of your WELCH line to share costs of DNA testing. I have already done it all and am happy to share the results with you.

    I would also like to see if you are interested in getting involved with a recently formed group of 120 people with shared genealogy going back to the early founders of colonial Maryland (primarily originating in Anne Arundel Co), all of whom have been DNA tested and uploaded to gedmatch.

    A relative of mine has been working with some close collaborators and they are in the process of analyzing the pedigree structure (686 individuals total, connecting 31 progenitors to the 120 contemporaries, which you can be made part of), and plans are to do a systematic DNA analysis.

    Please advise via email.


    Jim Welsh


  3. Hi Jim – I’m wondering if you might be willing to elaborate quite a bit on the process you demonstrate here for us enthusiastic hobbyists. I get the general gist of the concept, but would dearly love some insight into how you got here – this seems like mostly data and results with very little of your usually thorough explanation (and I must confess, compounded by I’m not familiar with a couple of your abbreviations here). I’ve been searching for a “set-up post” that I might have missed preceding this one without success. I’d really like to understand better what led you to this analysis – this seems too important a potential technique for me to give up on. Thanks for so generously sharing your talents and experience with us!


    • Andrew, The background is this: you can make a Triangulated Group (TG) of shared DNA segments – no genealogy required – it’s all a mechanical process. You can also find Common Ancestors (CA)by comparing your Ancestors to the Ancestors in someone else’s Tree. But the catch is that finding a CA with a Match in a TG DOES NOT MEAN that the shared DNA in the TG came from the CA! In almost all cases it’s possible to have multiple CAs with a Match (you just need to go back far enough). And as a TG builds up with a number of Matches, we often find one CA with one Match and another CA with another Match in the same TG. If the CAs are in the same ancestral line for you, then this is good news – another clue that you are on the right track to the correct CA line for the TG. But in many cases (to which I can attest based on my experience), the multiple CAs found with Matches in the same TG are from different lines. Each segment of your DNA can only come down one specific line of ancestors to you. It cannot “hop” from one line to another. So if you identify multiple CAs from different lines in a TG, something is wrong. Well not wrong – you can still be related by genealogy to all of them, but you cannot be related on the shared DNA segment from multiples line. So how do we resolve this? We either find 4 or 5 Matches in a TG who are all cousins on the same CA; or we find 4 or 5 Matches in a TG who are all cousins on the same ancestral line (walking the ancestor back). The more Matches you can find in a TG who got the shared DNA segment from the same Ancestor, the higher the probability that it is the correct ancestral line. Jim


  4. Pingback: The MRCA Knothole! | segment-ology

  5. This week I tied two generations to make a match with correspondence. He provided me three more generations back in one line and five generations back hopping the ocean with documentation all the way that is now being supported by dna and sticky segments. He threw in a second wife for my 4th ggrandfather and the knowledge of nine more half-cousins. That was this morning. I was able to find names for two of them in some paper trails with their linking surnames. In the process I discovered oddles more surnames for four children from first wife. Looks like I am going to be able to find CA for several steps up the line.


  6. Jim, this is your cousin PDJ. I just want to say I appreciate your getting in touch because I am learning so much from you about DNA and how to use it. I have a ways to go in learning how to apply this info but am making some progress. In the interim I am getting more family members, cousins etc to do the testing and will lead to some answers.

    Liked by 1 person

    • Well you now have one segment, at least, linked to an ancestral line. New Matches are pouring in – it’s hard to keep up with the influx of data… And, yes, testing cousins is one of the best things you can do to make more sense of all this. Good luck – that helps a lot too;>j Jim


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