How do I review a DNA Match?

To review a DNA Match, users can access an in-depth page presenting detailed information. This page includes contact options for the match, an estimated relationship, and sections such as Smart Matches, shared ancestral surnames, and shared DNA Matches, which indicate genetic relatives common to both individuals. Pedigree charts display up to five generations of direct ancestors, and the Chromosome Browser visually represents shared DNA segments, helping to identify common ancestors.

How do I use the Chromosome Browser — One-to-many?

The Chromosome Browser — One-to-many enables the comparison of DNA segments between a user (or individuals whose DNA kits are managed by the user) and up to seven DNA Matches. By analyzing these shared segments, including triangulated segments, users can infer relationships and identify common ancestors. This tool is accessed through the DNA Tools section of MyHeritage and allows for detailed visual comparison of genetic overlap across chromosomes.

What are the privacy options for my DNA data?

Users control their DNA privacy settings through the DNA Preferences section of their family site. These settings include enabling or disabling DNA matching, allowing others to view ethnicity estimates, and granting permission for DNA matches to view and download shared DNA segment data. Additionally, users can choose whether to display DNA badges in family trees and can opt into or out of the DNA Informed Consent Agreement, which allows MyHeritage to use anonymized DNA data for research. These options empower users to manage how their genetic information is shared and utilized on the platform.

How can I find triangulated DNA segments?

Users interested in triangulated DNA segments can compare themselves, a known relative, and a DNA Match in the One-to-Many Chromosome Browser. MyHeritage also helps identify triangulated segments on the Review DNA Match page, where an indicator shows when a match and a shared DNA match have triangulated segments with the user. Clicking this indicator automatically loads the comparison in the Chromosome Browser for efficient review. Alternatively, users can export shared segment data for all DNA Matches and manually look for additional matches with segments at the same genomic location.

What does the Whole Genome Sequencing (WGS) upgrade mean for my DNA results?

MyHeritage DNA has upgraded to Whole Genome Sequencing (WGS), which reads nearly all of an individual's DNA for improved accuracy in DNA Matches and ethnicity estimates. Previously processed kits or uploaded DNA data will not be reprocessed with WGS, and individuals must order a new kit to access this technology. While the sample collection kit remains the same, the processing method in the lab has changed. Significant improvements from WGS will become noticeable over time, as MyHeritage builds a larger database of WGS-processed kits.

Centimorgans: The One Number Defining Your DNA Matches

Receiving your DNA test results is a thrilling moment. But as you scroll through this long list of potential relatives, a fundamental question emerges: how are you actually related to all these people? The key to unlocking this mystery lies in a single, crucial number provided with every match: the amount of shared centimorgans. A centimorgan (cM) is the unit of measurement for shared DNA, and understanding what it signifies is the first step in transforming a list of names into a rich, detailed story of your family history.

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Key Takeaways

A centimorgan (cM) is a unit of genetic linkage used to measure the length of DNA segments you share with a match.
The total number of shared centimorgans is the most reliable indicator of how closely you are related to a DNA match; a higher number generally means a closer relationship.
While the cM value provides a probable relationship, it often falls within a range that could represent several different connections. Additional context is needed for confirmation.
Factors like the ages of both individuals and the number of shared DNA segments provide critical clues that help narrow down the possibilities.

What Exactly Is a Centimorgan?

A centimorgan is a unit used to measure genetic linkage. Think of it not as a physical distance, but as a measure of probability. It represents the likelihood that a specific segment of DNA on a chromosome will be passed down from an ancestor to a descendant intact through the generations. Our DNA is organized into 23 pairs of chromosomes, and we get one chromosome from each pair from our mother and the other from our father. For genealogical purposes, we primarily focus on the first 22 pairs, known as autosomal DNA, which you inherit from a wide range of all your recent ancestors.

This process of inheritance isn’t as simple as getting a perfect copy. Each generation, a process called genetic recombination shuffles the parental DNA. This means that the DNA you pass on to your children is a unique mosaic of the DNA you received from your parents. Because of this shuffling, the long, continuous segments of DNA inherited from a particular ancestor get broken into smaller pieces with each successive generation.

Centimorgans measure the total length of all these surviving identical segments that you share with another person. The more cM you share, the greater the amount of your DNA that has come from one or more recent common ancestors, strongly suggesting a closer relationship.

A centimorgan (cM) is a unit of genetic linkage used to measure the length of DNA segments you share with a match.

Decoding the Numbers: How Centimorgans Predict Relationships

The amount of shared DNA decreases by approximately half with each generation of separation from a common ancestor. Centimorgans provide a more granular way to express these percentages. While the amount of DNA inherited from any specific ancestor is important for genetics and can vary due to the random nature of recombination, specific relationships tend to fall within predictable cM ranges.

Typical cM Ranges for Family Relationships

Here is a general guide to expected shared cM values for common relationships:

Parent / Child: ~3300–3700 cM
Full Sibling: ~2200–3400 cM
Grandparent / Grandchild: ~1300–2200 cM
Aunt / Uncle / Niece / Nephew: ~1300–2200 cM
First Cousin: ~550–1200 cM
First Cousin Once Removed: ~220–700 cM
Second Cousin: ~75–400 cM
Third Cousin: ~30–200 cM

As you can see, some ranges overlap considerably. This is why the cM value alone is a powerful starting point, but not the final word. It provides a set of probabilities, guiding you toward the most likely connections to investigate further. The wide range for full siblings, for example, is a direct result of recombination; one sibling might randomly inherit more of the same specific DNA segments from their parents than another.

Shared Segments vs. Shared Centimorgans

When viewing a DNA match, you will typically see two key metrics: the total shared cM and the number of shared segments. While the total cM value is the primary indicator of the relationship's closeness, the number and size of the segments also provide valuable clues. Generally, closer relationships are characterized by a smaller number of much longer segments of shared DNA. More distant relationships, on the other hand, often result from a larger number of very small segments.

Imagine a beautiful ancestral quilt. Your great-grandparent’s contribution is a large, solid-colored piece of fabric. Your grandparent inherits about half of it, still a large piece. Your parent inherits half of that, a smaller but still substantial piece.

By the time it gets to you, that original fabric is a smaller patch. Now, consider your third cousin. Their patch comes from the same great-grandparent’s fabric, but it was cut and re-stitched through a different family line. You both have patches from the same original quilt, but they are identically-by-descent segments that were co-inherited.

A long, unbroken shared segment is a strong sign of a relatively recent common ancestor because there have been fewer generations for recombination to chop it up.

A centimorgan is a unit used to measure genetic linkage.

Navigating Complex Scenarios in DNA Analysis

While cM charts provide a fantastic roadmap, the genetic landscape has unique features that can sometimes be misleading. Understanding these edge cases is crucial for accurate analysis and is a cornerstone of responsible genetic genealogy.

The Challenge of Endogamy

Endogamy refers to the practice of marrying within a specific social group, religion, or ethnic community for many generations. This is common in populations such as Ashkenazi Jews, French Canadians, and some island or tribal communities. Over centuries, this practice means that everyone in the community becomes related to one another in multiple, distant ways.

For a genealogist, this creates a challenge. A DNA match from an endogamous population might share a higher-than-expected cM value, not because of a single close relationship, but because of dozens of very distant shared ancestors. The total shared DNA is inflated, making a fifth cousin appear genetically like a third cousin.

When Cousins Share No DNA

It might seem counterintuitive, but it’s entirely possible to have a genealogical cousin with whom you share absolutely no detectable DNA. By the time you get to third or fourth cousins, who share great-great or great-great-great-grandparents, the probability game kicks in. There is a small but real chance that you and a known fourth cousin simply didn’t inherit any of the same DNA segments from those distant ancestors. This is one of the more surprising truths of genetic genealogy, and it underscores that a lack of a DNA match doesn’t necessarily disprove a distant relationship found in historical records.

Beyond the Number: Why Context Is Everything

The cM value is a probability map, not a GPS coordinate. Several other data points are essential for interpreting your match correctly.

The Importance of Age

First, consider the ages of both individuals. Age can provide powerful clues and help rule out certain relationships immediately. For example, if you share 1750 cM with a match who is the same age as you, they can be identified as a probable half-sibling, not a grandparent. If a match is 40 years younger and shares 900 cM, they cannot be your first cousin but are a strong candidate for a first cousin once removed (your first cousin’s child). MyHeritage makes this process easier with features like the cM Explainer™, which integrates the ages of both parties to show the probability of each likely relationship and even diagram the potential paths to your most recent common ancestor.

Analyze Shared Matches

Second, look at your shared matches. This is one of the most powerful features available in genetic genealogy. By seeing which other people you and your match both share DNA with, you can begin to cluster your matches into family lines. For example, if you recognize a known maternal first cousin in the shared match list with an unknown match, you can immediately deduce that this new match is from your mother’s side of the family. You can take this a step further: if you know that first cousin is from your maternal grandmother’s side, you have now narrowed down the unknown match to a specific quadrant of your family tree. This cluster method is one of the most effective research habits you can adopt.

Confirm with Historical Records

Finally, the DNA evidence must be confirmed with traditional documentation. Use the clues from your DNA matches to guide your search through collections of historical records. Did your DNA match mention a great-grandmother with a unique surname who lived in a specific county? Search census records, such as Canada's 1931 Census, to find families with that name in that location. Can you find a death certificate that lists parents' names confirming a proposed common ancestor? Can you locate a passenger list that places two different family branches in the same city arriving in the same year? This is how you transform a genetic hypothesis into a confirmed family connection. By leveraging the full potential of a robust research platform, you can seamlessly pivot from a DNA match to searching billions of historical documents.

Putting It All Together

Understanding centimorgans is an essential skill for anyone serious about using an autosomal DNA test to explore their family history. This single number is the compass that points you in the right direction, helping you prioritize which matches to investigate and what kind of relationships to look for. It transforms what could be an overwhelming list of strangers into a solvable puzzle of cousins, aunts, and great-grandparents.

While the science behind it is complex, the practical application is straightforward. Use the shared cM value to form a hypothesis, then use age, shared matches, and family trees to test it. With patience and methodical work, that one critical number can lead you to a new branch of your family tree and uncover stories you never knew existed. Your heritage is waiting to be uncovered, one centimorgan at a time.