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Categories: DNA

This page was recently discussed in G2G. -- Whitten-1 14:20, 29 April 2019 (UTC)


Requirements for Triangulation

Simple one-to-one DNA confirmation is sufficient if your match is a third cousin or closer. Confirming relationships using more distant cousin matches requires triangulation. Three or more cousins need to all match each other on a single segment of DNA that is at least 7cM long. Seven cM is a bare minimum and presumes that the cousins' relationship back to their most recent common ancestor(s) is well-documented.

The three-legged stool

Triangulation has been compared to a three-legged stool. The common ancestor or ancestral couple is the seat. The three lines to the cousins are the legs.

All three legs should meet at the seat, or if not, then no more than one generation below it. Having two of the legs meeting closer to each other (e.g. two first cousins and a fourth cousin) does not make a valid triangulation. The stool would just fall over.

Which Relationships to Mark as Confirmed

Using WikiTree's Relationship Finder, find the most recent common ancestor (MRCA) or ancestral couple. Each child-to-parent relationship back to the MRCA can be marked as Confirmed with DNA if the requirements are met and a proper source citation is included in each child's profile.

Do you include the MRCA?

  1. If there is a single MRCA — because the matches are half-cousins, i.e. descendants of half-siblings who share only a mother or only a father — each child-to-parent relationship back to and including the relationship to the MRCA can be marked as confirmed.
  2. If there is a common ancestral couple each child-to-parent relationship back to but not including the relationships to the ancestral couple can be marked as confirmed. The relationships to the common ancestral couple can be marked as confident.

Example Source Citation

Here is an example of what to add to the == Sources == section of each child with a parent marked "Confirmed with DNA" using triangulation:

* Paternal relationship is confirmed by a triangulated group on GEDmatch consisting of [[Roberts-7085|Peter Roberts]], [[Sjostrom-39|Kris Sjostrom]], and [[Collins-5366|Elizabeth Collins]], who share a 10.8 cM segment on chromosome 1. The most-recent common ancestors shared by all three are [[Archer-1070|Benjamin Archer]] and [[Pinder-47|Elizabeth Pinder]].

For privacy reasons:

  1. do not include start and stop points for chromosome matches, and
  2. if one or both of your matches are not on WikiTree, use their initials or another anonymous identifier instead of their names.


23andMe Triangulation

If all the test-takers are on 23andMe click on TOOLS, then click on DNA COMPARISON. Use the Compare tool to view the segments shared by all the cousins. Note the chromosome number where the segment is located.

AncestryDNA Triangulation

AncestryDNA does not allow you to see exactly which segments of DNA are shared by your cousins. Consider uploading your results to GEDmatch to enable chromosome segment comparisons to be made.

MyHeritage Triangulation

If all the test-takers are on MyHeritage click on DNA Matches. Choose a match and click Review DNA Match. Scroll down through your shared matches with that person and find matches that have a small chromosome browser icon to the right hand of the match's information. Click on this, which will take you to the One to Many Chromosome Browser and Triangulation tool. You can click the "Add or Remove DNA Matches" button to add more matches to the browser for comparison. Note the chromosome number where the segment is located and the segment's size in centimorgans (cM).

GEDmatch Triangulation

If all the test-takers have uploaded to GEDmatch, use their Triangulation utility, One-to-Many utility (for you and each segment sharing cousin) and/or the One-to-One Compare for each of the test takers in the triangulated group (TG). Find segments measuring 7 cM or more that you share (i.e. overlap) with two or more people who are all distant cousins to each other. The 3D Browser is also useful.

FTDNA Family Finder Triangulation

When you find that two of your documented distant cousins are matches on Family Finder, they may be candidates for distant cousin triangulation. Family Finder's Chromosome Browser can help you determine on which chromosome all of you match each other and whether the matching DNA meets WikiTree's requirements for DNA confirmation. Here's how.

  1. On your FTDNA Family Finder home page click on the the "Chromosome Browser" and select the two distant cousins with whom you want to compare DNA. Click on the "Compare" button to see the individual chromosomes and look for overlaps with both cousins on the same chromosome. If you move your cursor over a colored overlapping segment, a pop-up box will give you the details of the overlap. Note: screenshots can be helpful for capturing the details.
  2. Once you have found and verified that your selected cousins match you on the same chromosome and the overlap with each other is enough to meet WikiTree's requirements for confirmation, continue on to step 3.
  3. Contact your selected cousins and ask them if they would be willing to help with the triangulation and, if so,
    • Send them a copy of what you see on the Chromosome Browser about the matches, including the details.
    • Ask each of them to do step 1 on their own FTDNA account, selecting you and the other cousin and to send you a copy of the details of what they see on the Chromosome Browser.
  4. Compare the details from their results with yours and determine the amount of DNA that the three of you have in common on the designated chromosome.
  5. If the details from at least one of the selected cousins confirms that the three of you have a sufficient amount of DNA in common, you can use this triangulated group for confirmation.
  6. Mark parental relationships as confirmed as described in the "Which Relationships to Mark as Confirmed" section above.

Here is an example DNA confirmation statement:

* Maternal relationship is confirmed by a triangulated group on {{Family Tree DNA}} consisting of [[Kingman-271|John Kingman]], [[Brooks-4984|Denny Brooks]], and JG, who share a 13.73 cM segment on chromosome 15. These matches have been independently verified by John Kingman and Denny Brooks via the Family Finder Chromosome Browser. John and Denny are 4C1R; John and JG are 3C1R; JG and Denny are 4C2R. The most-recent common ancestors shared by all three are [[Brooks-4989|Joseph Brooks]] and [[Basinger-161|Dorothy Basinger]].

This page was last modified 14:20, 29 April 2019. This page has been accessed 6,842 times.