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I wanted someone to confirm my thoughts or give me some guidance.

I have uncovered a possible 1st cousin mystery dna match. (ancestry)( I know all my first cousins and no one has done a dna test.)

I had my Dad do a Dna test (Ancestry), his results suggest great grandparent/aunt/ uncle / half sibling. I share 683 centimorgans 38 segments, and my Dad shares 1340 centimorgans and 50 segments with the mystery person.

What makes this interesting is this person shares dna with us from both maternal and paternal sides.(my Dad's father/mother). I know this because I am aware of confirmed relationships.

I take from this that it's possible that:

  1. one of my aunts gave up a child.(unknown to us) .
  2. I do know that my grandfather's sister gave a child up probably in the 1920's.BUT the only way it could be this mystery person is if the father was somehow a relative of my grandmother. like her brother Right? (it could happen) .This scenario would make them double cousins and would inflate the shared dna by double?

Am I right to assume these are the only ways we can share both paternal and maternal dna in those amounts?

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  • Are you from an endogamous ethnicity, such as Ashkenazi Jews? That could affect the interpretation of the data.
    – Ellen Spertus
    Jul 9, 2018 at 17:10

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Firstly, do you have X chromosome matching data? If yes, it could be additional clue. Because male person has only one X chromosome and it is inherited from his mother. Secondary, there is great chart with the relationship probability. It can be seen here. So this mystery person is probably from group B, i.e. can be

  • half-sibling of your father (i.e. you half-aunt or half-uncle),
  • aunt/uncle or nephew/niece of your father (you could guess the relationship to you on your own).

I think it is most probably case.

Also please provide more data regarding this match: what is the age of you dad? This person? Maybe we could compare their birthdates.

What makes this interesting is this person shares dna with us from both maternal and paternal sides

I am not sure that you correctly interpreted the data. Of course, there is possibility that some person is related to both of your parents. But it is not common. Could you provide more precise data about numbers?

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  • My father is 84. I don't have his x chromosome data unless it's included in the raw dna data from Ancestry. I do not have any information on the mystery person. I have tried to contact mystery person several times. There is an option to view shared matches on Ancestry, Shared matches for my Father and Mystery include, a 1st cousin , a great nephew and multiple 2-3 cousins all from the paternal side. I have confirmed with several cousin that mystery person is on their matches, sharing about 30 centimorgans.
    – Lisa Sipes
    Apr 5, 2018 at 1:46
  • Shared matches with maternal family include a 3rd cousin , and a 1st cousin 3xr, (a great grandson of my dads uncle). I have confirmation from the 1c3xr that he shares 27 centimorgans with mystery person.
    – Lisa Sipes
    Apr 5, 2018 at 1:47
  • I have contacted one of the paternal 1st cousins for the amount of shared dna she has with mystery.
    – Lisa Sipes
    Apr 5, 2018 at 1:56
  • Dad and his paternal 1st cousin share 903 ctm, dad and maternal 1c3xr share 56 ctn
    – Lisa Sipes
    Apr 5, 2018 at 2:07

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