DNA Triangulation Checklist
The DNA Triangulation Checklist outlines the exact technical protocol needed to prove that a shared DNA segment is Identical by Descent (IBD) from a specific ancestor, rather than an Identical by State (IBS) coincidental match. Require 3+ mutually matching relatives before drawing DNA proof.
📥 Free Download: DNA Triangulation Checklist
Printable PDF format • 100% Free • Technical protocol for segment verification
Identical by Descent (IBD): Shared DNA inherited from a real common ancestor.
Identical by State (IBS): Shared DNA that matches by pure chance, most common under 7 cM.
Triangulation Rule: Minimum 3 individuals sharing an overlapping chromosomal window who MUST also match each other.
Step 1 — Identify a Candidate Overlapping Segment
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Select chromosome and base-pair positions
Record chromosome number and start/end base-pair positions (e.g. Chr 12: 45,000,000–62,000,000).
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Identify at least three matches sharing the segment
Three is the absolute minimum requirement to rule out chance coincidental matching (IBS).
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Confirm exact base-pair overlap
Verify that start and end positions genuinely intersect using a chromosome browser or DNA Painter.
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Enforce a strict 7 cM minimum segment size
Discard candidate segments under 7 cM as they carry a high risk of being identical by state (coincidental).
Step 2 — Verify Matches Share DNA With Each Other
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Check shared match (ICW) status between all members
Confirm that Candidate A matches B, B matches C, and A matches C. Three people matching you on the same spot without matching each other is NOT a triangulation group.
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Visually inspect overlap in a chromosome browser
Use GEDmatch One-to-One, FTDNA Chromosome Browser, or DNA Painter to visually verify segment alignment.
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Exclude non-matching overlapping candidates
Eliminate matches who overlap in location but do not match each other (false triangulation).
Step 3 — Connect Segment to a Documented Ancestral Line
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Find Most Recent Common Ancestors (MRCAs)
Cross-reference trees of all group members to find the common ancestral couple where their lines converge.
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Confirm paper-trail records for at least 2 matches
Verify birth, marriage, and census records connecting at least two members to the shared ancestral couple.
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Record assigned ancestral couple and birth years
Document the specific ancestor couple name and approximate birth years linked to the segment.
Step 4 — Document & Map the Triangulated Group
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Log segment details in your master spreadsheet
Record chromosome, start/end positions, cM length, and member profile links in your master log.
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Assign a confidence label (Confirmed / Probable)
Mark the triangulation group as Confirmed once documentary evidence and 3-way DNA matching align.
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Add the segment to your active chromosome map
Input the triangulated segment into DNA Painter to permanently map that chromosomal stretch.
Two people matching you on the exact same segment can represent maternal and paternal matches coincidentally occupying the same position on opposite chromosome copies. Require at least three mutually matching individuals before calling a segment triangulated.
DNA Academy - Quick Answers
What formats are your free templates available in?
Our templates are available as downloadable Excel/Google Sheets files (for digital tracking).
How do I use a research log effectively?
A research log helps you track which records you’ve searched, what you found, and what’s still missing. We recommend filling it out as you go, it prevents duplicate searches and helps you identify patterns. Our template includes columns for date, source, location, and findings.
Are the templates available in languages other than English?
Currently, our templates are in English only. We are exploring translations into Swedish, Spanish, and German based on user requests. If you need a specific language, contact us and we’ll prioritize it.