DNA matching results

+5 votes
My sister, half brother and I shared the same biological father. There is a person that has a DNA match in GEDmatch and Wikitree to my sister, half brother and my father but no DNA match in GEDmatch or Wikitree to me. How is that possible??
in WikiTree Help by John Nash G2G6 Mach 1 (12.4k points)
retagged by Dorothy Barry
Hi, John. You didn't mention the amount of shared DNA shown by GEDmatch that the person-in-question shows with your sister and half-brother. Knowing that--total shared, number of segments, and largest segment for both your sister and half-brother--would give us more info to work from.

BTW, there's no DNA matching on WikiTree. WT never sees anyone's results, so can do no comparisons. Members enter information on their own profiles about tests they've taken, and that propagates up, across, and down the tree based solely on which profiles connect to whom as indicated by profiles' parental relationships. The names and links listed under the "DNA Connections" pane in the right-hand column of profiles aren't DNA matches, but they do provide great research hints to go looking for matches.

3 Answers

+4 votes
What is the GEDmatch ID of that person?
by Peter Roberts G2G6 Pilot (726k points)
We should not be publishing gedmatch ids on G2G without the permission of the kit owner.
Please explain why one should not write a person's GEDmatch ID on G2G?  If the reason is GDPR related then why would it apply if the person is a non-EU resident?

Thanks and sincerely,
I said you should not publish it without permission. If you have their permission then fine. If not, then regardless of GDPR it is an invasion of someone’s privacy to post that type of personal information in a public forum without consulting with them first.
Would you please point me to where I can read more about not publishing a person's GEDmatch ID without their permission?

GEDmatch users can use GEDmatch's alias feature if they wish to protect their privacy.

Thanks and sincerely,

Personally I think this type of courtesy and respect for others applies beyond just gedmatch kit numbers. However, you may like to take a look at this paragraph in Gedmatch Security Policy: 

Use of Results 

The nature of genealogy research requires the exchange of information. That use must also be tempered by respect for the rights and privacy of other individuals. Anybody found to be using this Site in ways not consistent with this principle of human decency will be subject to an immediate ban with all their data removed. Examples include, but are not specifically limited to, spam mailing lists or publishing other people's results or personal information without their permission. This principle also applies to the related or non-related persons included in Genealogy Data or other data uploaded to this Site. Determination of any violation of this principle will be at the sole discretion of GEDmatch administrators.

Another relevant reference is section 8 in the Genetic Genealogy Standards

Thank you for posting GEDmatch's Use of Results.  Publishing their GEDmatch ID is not the same as publishing their DNA results.  

Genetic Genealogy Standards section 8 says "Genealogists respect all limitations on reviewing and sharing DNA test results imposed at the request of the tester. For example, genealogists do not share or otherwise reveal DNA test results (beyond the tools offered by the testing company) or other personal information (name, address, or email) without the written or oral consent of the tester."  Again, publishing a GEDmatch user's GEDmatch ID is not the same as publishing their DNA results.


They gave examples of what should not be revealed without the written or oral consent of the tester. I suppose many people will put different interpretations on what is personal information, but I consider my gedmatch id to be just as personal as my name, address and e-mail.
Lynda and Peter,

Dealing with something very similar in my career for the last 40+ years and reviewing several Privacy rules here, on GEDMatch, and elsewhere, I believe that the GEDmatch ID number by itself, as long as there is no identifying information would not be a privacy violation issue. It's only when you combine the ID number with other personally identifiable information (such as true name, address, email, etc.) without the permission of that person, where it would become an issue.

I should be able to type in A138916 all day long without any problems.  I would also say that this type of policy should also apply to an GEDmatch alias used as long as it's not tied to any other personally identifiable information.

Personally, I probably wouldn't use a GEDmatch ID number and an Alias at the same time because of all the people/lawyers out there waiting to sue somebody for a perceived breach of these new regulations.
+8 votes
You, your sister, and your half brother each inherit about 50% of your own DNA from your father. But you each don't necessarily receive the same segments from him. So the match on GEDmatch and your half/full siblings likely each received the same segments passed down from your shared great ancestor(s), but you likely didn't inherit enough of the same segment from your father to match the individual on GEDmatch.
by Rick Peterson G2G6 Pilot (192k points)
The person in question also has a match with my half sister...my cousins, my father (my father never did a DNA test). Has no DNA segment match with me. At one time it did display a match with me on Wikitree but never showed up on GEDmatch. I suspect the person removed his DNA results from my profile and/or blocked it...
Does your half sister that matches the GEDmatch "person in question" also share your biological father? And your cousins that match that individual on GEDmatch, are they biologically related to you through your father (vs your mother)? If so (even though your father never tested), it still appears to me that you all probably share with that GEDmatch individual a common ancestor through an ancestral line that is shared by your father and your cousins. And even though you weren't identified as a DNA match to the GEDmatch individual, it doesn't mean that you're not related to that individual. It's likely that you just didn't inherit enough of the same DNA from the shared common ancestor for DNA matching to suggest your relationship to the individual.
My cousins father is the brother of my father. Half sister, half brother, sister and myself share the same biological father. The person in question has the largest cM with all of the previous persons is 27cM. Total segments is 41cM. I do not appear anywhere on his list in GEDmatch according to his GEDmatch id. He does not appear on my GEDmatch id either. I do a one to one comparsion between the person and myself and it display 0 segments found.
Are you relying only on the 'One-to-many' DNA comparison?  Keep in mind that the list generated cuts off after the first 2000 matches.  Smaller matches may not appear on the list.  Do a 'one-to-one' comparison.
I did a one to many and half sister, sister, half brother, cousin appear in his top 20 matches. I did a one to one comparsion for mine and his as I stated before.

"At one time it did display a match with me on Wikitree but never showed up on GEDmatch. I suspect the person removed his DNA results from my profile and/or blocked it..."  Please understand that Wikitree does not perform DNA matching.  When a Wikitree user adds info about a DNA test to their profile, that info populates all related persons/profiles within about eight generations in the DNA Connections section.  It is not possible for anyone else to remove or block DNA info from your profile.  Just because their DNA info showed up on your profile at one time doesn't mean that you had a DNA match with that person; it is only a possibility and any match must be determined on the DNA host site (Ancestry, GEDmatch, 23andMe, etc).  If the person's DNA test info appeared on your profile at one time and doesn't now, the most likely reason is that the other person's profile became Unlisted and the DNA info was removed from Wikitree.

If the person matches one of your siblings at 41 cM, that is around the average for a 4th cousin or 3C1R.  The odds of you not sharing any detectable DNA with a 4C or 3C1R is 30% (https://isogg.org/wiki/Cousin_statistics), a fairly common occurrence. 

+8 votes
You share about 50% of the same DNA with your sister, and 25% with your half-brother, and only 1/2 of this came from your father.  Depending on how distant the cousin is who is a DNA match, it is quite possible, even likely, that you all won't match him/her because you all received different segments of DNA from your father.  One thing you can say about the cousin is that he/she is related to you through your father.
by Kerry Larson G2G6 Pilot (240k points)

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