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I've been in search of my deceased father's biological family. He was placed for a closed adoption 60+ years ago. I've discovered the two families who parented him thanks to Ancestry DNA matches. We've been able to narrow it down further on one side to a woman who I thought likely mothered him. Her past and looks fit perfectly down to the year she placed a baby for adoption.

This woman's biological son took a DNA test to confirm our relationship. He's only showing up as a 519 centimorgan match across 25 segments. This is matching at about the same level as my father's 1st cousins (my first cousins once removed). Is there still a chance he's my half uncle at these levels or a way we can confirm our relationship further?

I'm female and an only child. Based on the results, I'm leaning towards him actually being a 1st cousin to my late dad but the coincidences of his mother's past are uncanny. The chart levels I've been referencing show the half uncle/niece relationship falling between 540-1175cm, so we are just under that.

For further reference here: This man has another confirmed half brother from a different side (unrelated to my side) and he's only matching 1272cms to him which was at the low level of half siblings. Chart levels for half siblings are usually between 1320-2100cm. Perhaps this man is at the low level with his half brother and me??

Two of my other close matches for first cousins once removed, from the same family, are showing at 422cm across 16 segments and 416cm across 21 segments. I have one other first cousin once removed from the other side of my father's family coming in at a slightly higher level of 565cm across 25 segments.

I've done a 23 and Me test but he has not. This is all strictly from Ancestry results.

  • What are your ethnicities? – Ellen Spertus Jul 28 '18 at 17:35
  • We are of Western European origin, Great Britain, and Irish ethnicity. – HayHay54 Jul 28 '18 at 21:55
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According to the relationship chart from Blaine Bettinger's Shared cM Project (2017), the 99% range found for a half aunt/uncle was 500-1446 cM. The full report (p. 3) aggregates data into clusters, combining:

  • first cousin
  • half aunt/uncle/niece/nephew
  • great-grandparent/great-grandchild
  • great aunt/uncle/niece/nephew

The range of the 99th percentile is 486-1761 cM. Both sets of data indicate that the man could be your half-uncle.

On the other hand, Bettinger's full report also breaks down data by company. Of the 70 half aunt/uncle/niece/nephew relationships, 90% had matches of 555-1209 cM (p. 24). (Bettinger does not provide data here on the outliers.) While it still is possible that the man is your half-uncle, it is far from definite. Chances are a little better if you're from a non-endogamous population and worse if you're from an endogamous population, such as Ashkenazi Jews.

My advice would be to export the data from Ancestry to GEDmatch, where you can analyze it more thoroughly, such as adjusting the minimum shared cM to use for a segment. You could also do an X-DNA comparison. If the man is your half-uncle, he and your father should have inherited all of their X-DNA from the suspected mother, and one of your X-chromosomes is from your father.

Good luck! Let us know what you find.

  • I will see if the uncle in question is interested in uploading our raw data to GED Match for further analysis. – HayHay54 Jul 28 '18 at 22:02
  • I was working on the X chromosome idea last night on 23 and Me. Unfortunately, the possible uncle in question hasn't done a 23 and Me test. However, one of his male first cousins has. This cousin of his shares half my X chromosome. The cousin's mother is the sister of the woman we believe to be my grandmother. This stands to reason that my father must have inherhited his X from the female line of this family and passed it to me, correct? If that's the case, I guess the mystery is solved as the only other person who could have parented my father in this family was a man. – HayHay54 Jul 28 '18 at 22:03
  • Thank you. I'm still in awe of the low centimorgan match even though all signs point to him being my uncle. I was expecting more like an 800 range, but the X chromosome doesn't lie. – HayHay54 Jul 28 '18 at 22:06
  • @Hayley54 The Ancestry DNA test includes X-chromosome, so your suspected half-uncle doesn't need to do another test, just export it to somewhere more powerful. – Ellen Spertus Jul 28 '18 at 23:38
  • Export it to say GED match then? I have seen in a couple places people mention that Ancestry doesn't factor the 23rd chromosome in their DNA data. Perhaps this is why he's coming in lower than I expected? – HayHay54 Jul 28 '18 at 23:48

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