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I took an AncestryDNA test and have matched with a new relative JP. She and I share 1836cM. She’s not my half sister. She’s not my grandparent. She could be my father’s half sister. With this amount of DNA in common though, she should be a full Aunt not half. I share 1102cM with her daughter. I’m looking into her as an aunt, but I don’t want to dig too deep in the wrong direction.

Can cM’s show up outside of the standard range and be accurate?

Also, I had my mom take a test to see if JP is her sister, they are not a match but have many relatives in common.

  • Can you explain a little more about the matches JP and your mother have in common? Are they close matches. Do you know how they are related to your mother? Could your mother and father be distantly related? You can upload your AncestryDNA data to Gedmatch. There is procedure there to measure how closely your parents are related. – Bill Sep 17 at 22:12
  • I have done the Gedmatch assessment and found that my parents are distantly related. The matches that my mom and JP share are predominately 2nd cousins to my mom. I don’t know their relation to JP because I can’t see her side of things. One 1st cousin once removed to JP is a 4th cousin to my mom. – Naja Sep 18 at 13:50
  • It would help to get JP to share her matches with you. Who she matches and how strong the matches are might help solve your mystery. – Bill Sep 18 at 20:28
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The straight forward answer to your question is that JP can be one of the following

  • Half Sibling
  • Aunt/Uncle/Niece/Nephew
  • Double First Cousin
  • Grandparent/Grandchild

The chart at the bottom of this page from the Shared CM Project will tell you more about the range of CM's seen for each category. If someone appears to be outside those ranges then the best thing to assume is that you have guessed the wrong relationship, not that the match is outside the observed range. There is a small chance that it could be outside the known ranges, but it is very much not the first thing you should assume.

I would suggest only using the match size as a rough guide to relationship. Unless it is a parent-child relationship it is always an ambiguous clue. To actually find out how JP is related to you, look more at her other matches. She is obviously related to you on your father's side. Does she have matches to cousins on your father's mother's side and to cousins on your father's fathers side. She might have a parent that is not related to you. If so she could have strong matches that are not in common with you. Use those to figure out who that non-related parent is and that might give geographical/time clues as to who the related parent is.

  • I don’t have any known relatives in my father’s family that have taken tests, so I have no idea. My father’s biological father is a mystery, which is why she could be a half Aunt. – Naja Sep 17 at 20:32
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    The range for a half aunt/uncle is 500-1446 cM. 1836cM is really too far out of that range. – Bill Sep 17 at 21:55
  • That’s what I was thinking. But I can’t find a logical relationship for JP other than that of half aunt. – Naja Sep 18 at 13:51
  • Does it matter that our match is across 95 segments? Does that help make one relationship more or less possible? – Naja Sep 18 at 13:58
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    No, the number of segments is not really significant for larger matches. For small matches it can be helpful. – Bill Sep 18 at 20:22

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