No Match With the Parents of a DNA Match?

What does it mean if you don’t match either parent of your DNA match?  What if your match doesn’t match either of your parents?  Does it mean that you aren’t really related? 

What are the possible explanations for this phenomenon?  As it turns out, this is a common occurrence, especially with matches with whom you share a very tiny amount of DNA. 

In this post, I’ll explain some of the reasons that you might not show up as a match for either parent of your DNA matches.

Possible reasons you don’t match either parent of your DNA match, or they don’t match your parents

The following are the most common reasons that you don’t show up as a match to either parent of your DNA match, or your DNA match doesn’t match either of your parents.  These reasons are most applicable to matches with whom you share only a tiny amount of DNA.

Also, for the purposes of this article, I am assuming that you know for a fact that you are descended genetically from your parents, and there is evidence of the same for your DNA match.

You are not really related to the DNA match if you don’t also match parents

The most likely reason that you don’t show up as a match to the parents (either or both) of your DNA match is because you are not really related to your match.  This is most likely to be the case when the DNA segment you share with your match is very small, like less than 5-7 centimorgans (cMs). 

The probability of a false positive match shrinks as the size of shared DNA segments grow, but it is still possible to share a 10-15 cM segment that is not identical because it was inherited from a common ancestor.

There are two important terms to know when learning about DNA segments that are inherited, and whether or not they are indicative of a common ancestor. 

Identical by descent means that you have a DNA segment that matches someone because you inherited it from one of your parents, and your parent inherited it through their parent from the common ancestor that you share with your DNA match.

It is possible to have a DNA segment that is identical to one shared by someone else without being related to that individual.  These coincidentally identical segments are called identical by state – meaning that they just “are” identical. 

If you have access to your parents DNA and neither of them match a DNA match who shares a small segment with you, then there is a good chance that the segment that you and your DNA match share is just identical by state.

Everyone involved tested at different DNA testing companies

Every DNA testing company uses different technologies to test DNA samples.  The differences in technology can range from the type of equipment used, to the proprietary software used to determine your results. 

Additionally, each company tests difference numbers of SNPs (single nucleotide polymorphisms).  Each human has millions of SNPs, but only a small portion of these are tested during autosomal DNA testing. 

Comparing SNPs is the best way to spot genetic differences between humans, which is why they are useful for determining and estimating genetic (and genealogical) relationships between two individuals. 

Comparing SNPs is the best way to spot genetic differences between humans, which is why they are useful for determining and estimating genetic (and genealogical) relationships between two individuals. 

Note: There is not really a “best” number of SNPs to test, and I definitely wouldn’t choose a testing company based on the number of SNPs that they test.  I would say that the size of the DNA testing database, customer service, and price are more important factors, especially if you are testing to look for DNA matches to build your family tree.

If you tested at a company that tests more SNPs, or just slightly different SNPs, than the one where your parent tested, there is a small chance that you might have a few extremely distant matches that show up for you, and not for your parents. 

This can happen, for example, if you did your test with My Heritage and your parents did their test with Family Tree DNA and uploaded their results to My Heritage, or if you tested with Ancestry, and your dad tested with 23 and Me, and your mom tested with My Heritage DNA, and you all upload your DNA to Gedmatch.  Or any number of combinations of ways where everyone involved ended up with their DNA on the same site, but initially tested with different companies.

Should not matching the parents of my DNA match affect my research?

Not matching either parent of your DNA match (or finding a match that doesn’t match either of your parents) is most likely to happen with very small DNA segments, which means that even if the match was really related, they are likely related so far back that it would be almost impossible to spot your common ancestor. 

This means that this situation should not affect your research at all.

Remember that the closest matches are most closely related to you, and will your research much more than the distant ones.

Most people should have an ample supply of much closer matches, who share less distant most recent common ancestors.  If you are very concerned about these smaller matches that don’t match either of your parents, you can look into “phasing” your DNA matches with the DNA of at least one parent. 

If you can phase your DNA matches with your mother’s DNA, for example, then you can eliminate these “false” matches on your mother’s side.  If you have DNA from both of your parents, then you can phase matches on both sides, and you can feel fairly confident that all of your matches – even those most distant ones – are legitimate.

Conclusion

I hope that this post has helped give you a few ideas as to why your DNA doesn’t match either of your parents, or vice versa, and how you can go about focusing only on the matches that can help you research your tree. 

If you have any questions or comments about something that you have read here, I would love to hear from you in the comments below.

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