DNA Chromosome Browser: Visualize & Compare Shared Segments

By Peter Salenius Published: Updated:
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All segment parsing, chromosome bar plotting, and overlap computations are executed 100% locally in your web browser. Your genetic data, chromosome coordinates, and match names are never uploaded, saved, or transmitted to external servers.

1. What is a DNA Chromosome Browser and Why Do You Need One?

When you view your DNA match list on commercial platforms like AncestryDNA, 23andMe, or MyHeritage, your relationship is initially summarized by a single number: total shared centimorgans (cM). While shared cM indicates roughly how closely related you are (e.g., 200 cM suggests a 2nd cousin, 1st cousin twice removed, or half-great-aunt), it provides no information about which specific ancestor passed down that DNA.

A DNA Chromosome Browser expands your research from one-dimensional summaries into two-dimensional genomic mapping. By plotting shared DNA segments onto visual models of Chromosomes 1 through 22 and X, a chromosome browser reveals the exact physical locations (start and end base-pair coordinates) where you and your matches share identical blocks of genetic code.

Moving From Match Lists to Segment Evidence

Visualizing shared segments allows genetic genealogists to accomplish four critical tasks:

  • Map Ancestral DNA: Assign specific chromosome segments to identified ancestors or ancestral couples (e.g., "Chromosome 4, 15 Mb–45 Mb was inherited from Great-Grandparents William and Sarah").
  • Identify Candidate Overlaps: Spot regions where multiple matches overlap on the exact same physical stretch of a chromosome.
  • Validate Triangulated Groups: Test whether overlapping matches share DNA from a single common ancestor or represent separate ancestral lines.
  • Distinguish IBS from IBD: Filter out tiny, identical-by-state (IBS) segments that represent general population noise rather than recent genealogical inheritance.

Platform Capabilities & Chromosome Browser Comparison

Not all commercial DNA databases provide native chromosome browsers. The table below compares segment mapping features across major testing services as of late 2026:

Testing Platform Native Browser? Triangulation Indicators? Raw Segment Export? Key Notes & Upload Policy
MyHeritage DNA ✅ Yes (Up to 7 matches) ✅ Yes (Framed overlap regions) ✅ Yes (CSV export) Supports uploaded raw data (one-time unlock fee for advanced tools). Excellent triangulation features.
FamilyTreeDNA (FTDNA) ✅ Yes (Up to 7 matches) ⚠️ Partial (Matrix tool bucket) ✅ Yes (CSV export) Displays detailed segment tables. Autosomal transfer unlock retired in August 2026 for new uploads.
23andMe ✅ Yes (Advanced Comparison) ⚠️ Manual inspection ⚠️ Limited / Tier dependent Relaunched Advanced DNA Comparison for 23andMe+ Premium subscribers. Displays overlapping segments.
GEDmatch (Free + Tier 1) ✅ Yes (1-to-1 & 1-to-Many) ✅ Yes (Tier 1 Triangulation) ✅ Yes (Full CSV) Universal cross-platform database. Free 1-to-1 browser; dedicated automated triangulation in Tier 1.
AncestryDNA ❌ No native browser ❌ No segment coordinates ❌ No segment export Does not reveal start/end positions. Users must download raw DNA and upload to GEDmatch or MyHeritage.

2. How to Use the Genetic Voyage DNA Chromosome Browser

Our free interactive chromosome browser is designed for maximum ease of use and flexibility. Follow these simple steps to plot your shared segments:

  1. Export Segment Data: Download your segment file (CSV format) from 23andMe, MyHeritage, FTDNA, or GEDmatch. Alternatively, copy the downloadable table containing your matches' chromosome details.
  2. Input Data into the Tool: Paste your raw CSV data into the input box or click "or upload a CSV file..." to select the file directly from your device.
  3. Automatic Column Detection: The tool automatically recognizes standard header names for Chromosome, Start Position, End Position, Centimorgans (cM), SNPs, and Match Name.
  4. Click "Draw Chromosome Browser": The browser renders visual bars for Chromosomes 1 through 22 and Chromosome X, drawn to scale according to GRCh38 genomic lengths.
  5. Interactive Match Filtering: Click any match tag in the legend to toggle individual matches on or off, instantly updating the visualization.
  6. Analyze Overlap Zones: Check the "Highlight overlapping segments" option and adjust the minimum overlap slider (e.g., 1 Mb or 5 Mb) to isolate candidate triangulated regions across multiple matches.
🔒 100% in your browser — your DNA data is never uploaded anywhere

DNA Chromosome Browser

Paste your segment / chromosome-browser data and see exactly where your matches overlap on each chromosome

Export your shared-segment or "chromosome browser" data from 23andMe, FamilyTreeDNA, MyHeritage, or GEDmatch (usually a CSV or downloadable table with columns for chromosome, start position, end position, and cM) and paste it below. Everything is parsed and drawn directly in your browser — nothing is uploaded to any server, so it's safe to use with your real genetic data.

Accepted columns (any order, case-insensitive): Chromosome / Chr, Start Position / Start, End Position / End, Centimorgans / cM, SNPs (optional), Match Name / Name (optional).
Region shared by 2+ different matches

Overlapping regions

Regions where segments from two or more different matches cover the same stretch of a chromosome. Matches hidden in the legend are excluded.
Notes: Chromosomes are drawn to scale using standard reference (GRCh38/hg38) physical lengths, and segments are positioned using the start/end base-pair coordinates from your file — not converted through a genetic map, so positions reflect physical location rather than recombination distance. Overlap highlighting only shows where segments from different matches cover the same region; it does not prove that those matches are related to each other or share a common ancestor. This is a visualization aid, not a substitute for proper triangulation or genetic-genealogy software; always confirm findings with additional evidence (shared matches, family trees, documentary research).

3. Interpreting Results: Overlaps vs. True Triangulation

Understanding what your chromosome browser display shows—and what it does not show—is essential for avoiding false conclusions in genetic genealogy.

1. Visual Chromosome Bars & Match Segments

The main chart displays 23 chromosome rows (Autosomes 1–22 plus the X Chromosome). Gray background bars represent the full physical length of each chromosome in base pairs. Colored overlay blocks represent the exact segments you share with each tested relative. Hovering over or clicking any segment displays a detailed tooltip showing the match name, chromosome number, start/end base positions, segment length in cM, and total matching SNPs.

2. Candidate Overlap Regions (Amber Bands)

When the "Highlight overlapping segments" option is enabled, the browser scans all active matches using a sweep-line algorithm over unique boundary points. Wherever segments from two or more different matches cover the same physical stretch of DNA, an amber translucent band appears across the chromosome bar, and an amber zone is rendered in the dedicated overlap track directly below.

3. The Overlapping Regions Table

Below the visualization chart, the Overlapping Regions Table compiles a complete breakdown of every candidate overlap zone. For each chromosome, it lists:

  • Chromosome number and exact Start/End base-pair coordinates
  • Total physical overlap length in megabases (Mb)
  • Number of distinct matches sharing that overlap region
  • Color-swatch tags identifying all matches involved in the overlap
⚠️ Crucial Distinction: Candidate Overlap vs. True Triangulation
An overlapping region in a chromosome browser proves that Match A shares DNA with YOU and Match B shares DNA with YOU on the same chromosome region. It does NOT prove that Match A and Match B share that DNA with each other!

For example, if Match A is your maternal 2nd cousin and Match B is your paternal 2nd cousin, both will show an "overlap" on Chromosome 5 because you have two copies of Chromosome 5 (one from Mom and one from Dad). You match A on your maternal chromosome and B on your paternal chromosome.

To establish true triangulation, you must verify that Match A and Match B also match each other on that exact same segment (In-Common-With / matrix confirmation) and that the segment is inherited from a single common ancestral couple.

4. Scientific Methodology, Assumptions, & Limitations

Reference Genome Assembly Coordinates (GRCh38 / hg38)

The Genetic Voyage Chromosome Browser draws chromosomes to scale using physical base-pair lengths from the human genome reference assembly (GRCh38/hg38). Physical coordinates are universal across all testing services:

  • Chromosome 1: ~248.95 Megabases (248,956,422 bp)
  • Chromosome 7: ~159.35 Megabases (159,345,973 bp)
  • Chromosome 22: ~50.82 Megabases (50,818,468 bp)
  • Chromosome X: ~156.04 Megabases (156,040,895 bp)

Physical Base Pairs (Mb) vs. Genetic Map Distance (cM)

It is vital to distinguish between physical distance measured in megabases (1 Mb = 1,000,000 base pairs) and genetic recombination frequency measured in centimorgans (cM):

  • Physical Distance (bp / Mb): Measures the literal count of nucleotide letters along a DNA strand. Universal across all testing platforms.
  • Genetic Distance (cM): Measures the biological probability of recombination (crossing over) occurring during meiosis. On average in humans, 1 cM corresponds to roughly 1 Mb, but this ratio varies dramatically across genomic regions.
  • Recombination Hotspots vs. Coldspots: Near chromosome ends (telomeres) and recombination hotspots, crossing over occurs frequently—so a 5 Mb segment might equal 12 cM. Near chromosome centers (centromeres) and coldspots, recombination is suppressed—so a 15 Mb physical stretch near a centromere might equal only 4 cM!

Identical by Descent (IBD) vs. Identical by State (IBS)

Not all matching DNA segments represent recent ancestral inheritance:

  • Identical by Descent (IBD): Segments passed down unbroken from a genuine recent common ancestor. These segments are genealogically meaningful.
  • Identical by State (IBS) / Chance: Coincidental matching strings of genetic letters that occur by chance or represent ancient population-wide DNA shared across thousands of years.
  • Recommended Thresholds: Segments smaller than 7 cM (or ~5 Mb) have a high probability of being IBS noise. Genealogists should focus on segments larger than 7–10 cM for reliable tree building and triangulation.

The Necessity of DNA Phasing

Standard commercial DNA tests produce unphased data—a combined mixture of your maternal and paternal chromosomes. When unphased data is processed, the computer cannot distinguish whether a letter belongs to your mother's or father's strand. This can create "false crossover" segments where an algorithm hops between maternal and paternal letters. Testing a parent or using phased DNA kits (e.g., via GEDmatch phasing) eliminates false crossover matches and guarantees 99.9% IBD segment accuracy.

Adjustments for Endogamy & Pedigree Collapse

In endogamous populations (e.g., Ashkenazi Jewish, Acadian, Polynesian, or isolated island communities), intermarriage over centuries causes individuals to inherit multiple small segments from common ancestral lines. In endogamous research, total shared cM figures become artificially inflated. Genealogists working with endogamy must raise segment thresholds to at least 10–15 cM and focus strictly on multi-match triangulated blocks.

5. Practical Use Cases & Workflows

Case Study 1: Isolating an Unknown Great-Grandparent Line

Scenario: An adoptee seeking their biological maternal grandfather identifies three 2nd cousin matches sharing between 180 cM and 260 cM on MyHeritage. All three matches share trees pointing to a common couple: John Miller (1860–1925) and Mary Davis (1865–1940).

Workflow:

  1. The researcher exports segment CSV files for all three cousin matches and inputs them into the Genetic Voyage Chromosome Browser.
  2. The browser reveals a prominent 28.5 Mb amber overlap zone on Chromosome 7 (positions 23,456,789 to 78,345,678; ~32 cM) shared across all three cousins.
  3. By checking MyHeritage's In-Common-With matrix, the researcher confirms that all three cousins match each other on that exact segment, establishing a validated Triangulated Group (TG).
  4. Because all three matches inherit that specific Chromosome 7 block from John Miller & Mary Davis, the adoptee confirms that their unknown grandfather must be a direct descendant of the Miller/Davis couple!

Case Study 2: Mapping Paternal vs. Maternal X-Chromosome Inheritance

Scenario: A male researcher compares a 45 cM match on Chromosome X. Because biological males inherit their single X chromosome exclusively from their mother, this match must belong to the maternal line.

Workflow:

  1. The researcher pastes segment CSV data for three X-chromosome matches into the browser.
  2. The tool plots a 35 Mb segment on Chromosome X (positions 30,123,456 to 90,234,567) shared with two maternal 2nd cousins.
  3. Using X-chromosome inheritance rules (maternal grandfather passes his X intact to his daughter, without paternal recombination), the researcher narrows the candidate lineage directly to the maternal grandmother's ancestral lines!

6. Frequently Asked Questions (FAQ)

What is a DNA chromosome browser?

A DNA chromosome browser is a visual comparison tool that plots the physical positions of shared DNA segments on Chromosomes 1 through 22 and X. It allows genealogists to see exactly where on a chromosome they share genetic material with specific matches.

Is an overlapping segment the same as a triangulated group?

No. An overlapping segment in a chromosome browser shows where two or more matches share DNA with you on the same physical region. True triangulation requires confirming that those matches also share that exact same DNA segment with each other, inherited from a single common ancestral couple.

Which DNA testing platforms offer a native chromosome browser?

MyHeritage DNA, FamilyTreeDNA, 23andMe, and GEDmatch offer native chromosome browsers. AncestryDNA does not provide a chromosome browser or segment coordinates. To analyze AncestryDNA matches in a browser, users must upload raw DNA files to third-party databases like GEDmatch or MyHeritage.

Are my DNA segment coordinates kept private when using this tool?

Yes, 100%. All CSV parsing, segment drawing, and overlap calculations are performed locally inside your web browser using HTML5 and JavaScript. No genetic data, segment coordinates, or match names are ever transmitted to or stored on Genetic Voyage servers.

Why are chromosomes drawn using base-pair megabases (Mb) rather than centimorgans (cM)?

Physical base-pair positions from the GRCh38 reference assembly provide absolute genomic coordinates that are universal across all testing platforms. While centimorgans measure genetic recombination frequency, base pairs define the exact physical boundaries required for segment alignment and mapping.

8. Verified Scientific & Methodological References

  • ISOGG Wiki. "Chromosome Browser." International Society of Genetic Genealogy. Platform capabilities, segment visualization standards, and limitations.
  • ISOGG Wiki. "Triangulation." International Society of Genetic Genealogy. Methodology for establishing 3-way segment matching and ancestral attribution.
  • ISOGG Wiki. "Identical by Descent (IBD) vs. Identical by State (IBS)." International Society of Genetic Genealogy. Distinguishing ancestral segment inheritance from background population noise.
  • National Human Genome Research Institute (NHGRI). "Centimorgan (cM) Fact Sheet." Authoritative definition of recombination frequency and genetic mapping units.
  • Bettinger, Blaine. "The Shared cM Project v4.0." DNA Painter. Empirical dataset of observed centimorgan sharing ranges for known relationships.
  • Durand, E. Y., et al. (2014). "Reducing the computational cost of statistical phasing." PLoS ONE, 9(3), e93827. Mathematical principles of haplotype segment sharing and statistical phasing.
Don’t have segment data yet? Get AncestryDNA · Get MyHeritage DNA · Compare DNA tests. Want to estimate how a match is related? Try the DNA Relationship Probability Calculator.
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