I am a genetics beginner:

A little back story: My mother was adopted at birth. She found her birth mother and siblings back in the 90s. The birth mother was deceased at the time, and we also discovered that her brothers are ALL her half brothers. My mother was most likely the biproduct of a fling and no one on the bio mother’s side had a clue as to who my mother’s father was, factually speaking, they didn’t even know that my mother existed as the pregnancy was kept a secret from the family apparently. Anyways, I am the son of that adopted woman. Recently a relative that popped up on ancestry.com as a first cousin of mine, not on my fathers side of the house at all or on my mother’s mom’s side.

So here is where the confusion lies...I’m only 37, the relative is 63. My mother is also 63. They both know who their mothers are. They were born a month apart and geographically within 5 miles of one another (father was not named on birth certificate). I have managed to get all three of us into GEDmatch and the numbers in the relationships are as follows:

The genetic relationship by the numbers, according to GEDmatch.com:

My mother to me:

  • 1.0 generational gap

  • Autosomal DNA: total cM - 3587.1 cM, largest 285.1

  • XDNA: 196.1 cM, largest 196.1 cM

Relative in question, to me:

  • 1.9 generational gap

  • Autosomal DNA: total cM - 976.9 cM, largest - 99.1 cM

  • XDNA: 129.2 cM, largest 129.2 cM

My mother’s relationship to relative in question:

  • 1.5 generational gap

  • Autosomal DNA: total cM - 1822.5 cM, largest - 129.8

  • XDNA: 195.3 cM, largest 195.3 cM

    What I am seeking is a deeper understanding of what these numbers are saying. My conclusion so far is that the relative in question is either a a half-sister to my mother or her aunt/niece (paternally).

Which is it or is there not enough information?

  • This is unclear. Do you mean something like this: "she found her birth mother's family in the 90s (her birth mother was deceased by that time) and my mother's surviving siblings are all half-brothers"? Please disambiguate the places that say "she" and "her" so we can tell when you are talking about your mother and when you are referring to your bio-grandmother, and so on. – Jan Murphy Apr 15 '18 at 1:29
  • Jan, I’ll simplify this for you. What I’m trying to convey is that there are three individuals: A mother, a son and “X” relative. What is the relationship based upon the numbers provided for the mother and “X” relative? Everything I’ve read says Half-Sister or Aunt Niece. Im trying to find someone who could look at the numbers and see if there is a way to define that genetic relationship. Is the “X” individual a half-sister or an Aunt / Niece? Does that clarify the issue? – J.Huff Apr 15 '18 at 5:07
  • 2
    Unfortunately, DNA test can't explain the precedence of birth, so it is really indistinguishable if this person aunt or niece. Also in big families such thing happens when, for example, children from previous generation is younger than in next. For example, I am 30 old years, my uncle - 40, my daughter is 2 years, and his child will be born in May. And his child will be cousin to me. This skew with next generation may change slightly. – George Gaál Apr 15 '18 at 6:14
  • Have you looked at the other questions tagged DNA on the site? Do the answers to genealogy.stackexchange.com/a/13891/1006 or genealogy.stackexchange.com/q/13459/1006 help? – Jan Murphy Apr 15 '18 at 8:27

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