Understanding DNA Matches in Genealogy
Interpreting DNA results can be both fascinating and complex, especially when confronted with a reasonable DNA match that lacks shared centimorgans (cM) in autosomal results. This situation can lead to confusion, but a structured approach can help clarify the relationship between matches.
What Are Centimorgans (cM)?
Centimorgans (cM) are a unit of measurement used to describe the distance between genes on a chromosome. A higher cM value typically suggests a closer biological relationship. In autosomal DNA testing, which assesses chromosomes 1-22 (not including sex chromosomes), matches are calculated based on the amount of shared DNA. Generally, close relatives will share a higher amount of cM, whereas distant relatives will share less.
Why Might There Be No Shared cM?
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Testing Limitations: Not all DNA testing companies use the same reference databases or methodologies, leading to discrepancies in shared cM calculations. It’s important to ensure that the testing companies are compatible and utilize similar bases for measuring shared DNA.
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Small Segment Sharing: It is possible to share DNA segments that are too small to compute significance in terms of cM. Matches could indicate a distant relationship, where the shared DNA is present but not enough to be counted meaningfully in the results.
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Inaccurate Trees: Family trees are often built on assumptions or incomplete information. If a family tree is incorrectly documented, it may result in DNA matches that appear reasonable based on names or locations, yet still yield no shared cM.
- Cousin Complexity: Many people have multiple lines of ancestors and may share DNA with individuals through different familial connections. A person may have a reasonable match yet not share cM due to the complexities of cousin relationships and common ancestors.
Steps to Investigate a Reasonable Match
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Verify the Relationship: Begin by reviewing family trees associated with the DNA match. Look for common ancestors or shared surnames. Be diligent in checking both your own tree and the match’s tree for accuracy.
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Reach Out for Collaboration: Contact the match to discuss your genealogical findings. They may have additional information that can clarify the relationship. Collaboration can often reveal new insights into how two trees intersect.
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Examine Additional Matches: Look for other individuals who share a DNA match relationship with both you and the reasonable match. This can provide clues and help you understand the connection better.
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Use Third-Party Tools: Employ DNA analysis tools that can provide more insights into your matches. Websites specializing in DNA analysis can offer detailed views on shared segments and possible relationships.
- Patience and Persistence: Genetic genealogy is an ongoing journey of research. Keep an open mind, and be ready for unexpected discoveries through ongoing testing and ancestral exploration.
FAQ
Q: What should I consider if my DNA match has no shared cM?
A: Consider the possibility of small segment sharing, testing discrepancies, or inaccuracies in the family trees. Engaging with the match and utilizing third-party tools can help clarify the situation.
Q: How reliable is shared cM in determining relationships?
A: While shared cM provides a useful guideline for understanding potential relationships, it’s not definitive. It should be integrated with traditional genealogical research and family history for a more accurate interpretation.
Q: Can I still learn about my ancestry if a reasonable match shows no cM?
A: Yes, it is still possible to gain insights into your ancestry by examining family trees, collaborating with matches, and exploring additional genetic relationships through other matches in your test results.