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I have three 3rd cousins on my mother's side with 66.1-71 cM shared between us. One is male and 2 female. These 3 cousins are 2nd cousins to each other and I believe I am their third cousin. They each have a great grandparent that are siblings, the females have a male great grandparent and the male has a female great grandparent all having the same parents. I am looking for my mother's great grandmother and believe she is in this family.

Where would she fit?

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  • I would normally suggest using a DNA Painter "What Are The Odds" tree, but this is a case I've found doesn't work well - those trees are VERY good at telling you whether someone has the same common ancestor as a known cousin cluster, and sometimes which specific family, but since you're outside the known cluster, it's a lot more iffy.
    – cleaverkin
    Apr 16, 2019 at 21:53
  • Thank you for responding. I must make a correction, I am looking for my mother's grandmother. She shares 90, 82 and 74 cM with these cousins. The 3 cousins all have a grandparent that are siblings in addition to 1 having married a 1st cousin. More complicated, right? Anyway, I will keep digging, thanks again!
    – Mary Ann
    Apr 17, 2019 at 5:05

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Second cousins share one set of great grandparents. They would each have one grandparent who is the sibling of the other cousin's grandparents. If they are 2nd cousins as you say (and your saying their great grandparents are siblings was in error), and if you are actually the 3rd cousin of each of them, this means that your great grandparent was the sibling of one of their great grandparents.

If all the above is accurate, then your mother's grandparent is the sibling of those cousins' great grandparent.

Your mother's great grandmother (if that is the correct line) would be the great great grandmother of these cousins. This means that you would share one set of 2nd great grandparents with these cousins.

Of course that all assumes that you're really 3rd cousins to them (and that they're really all 2nd cousins to each other). According to the Shared cM Project, your DNA results are well within the range for 3rd cousin.

They are also within the range for:

  • 4th cousin
  • 5th cousin
  • 6th cousin
  • 3rd cousin once removed
  • 3rd cousin twice removed
  • 2nd cousin once, twice, or thrice removed
  • Half 2nd cousin
  • Half 3rd cousin

And many more variations. Check out the chart.

You're on the right track and the DNA evidence does seem to point to you being related to them through the great grandparents they share (triangulate your DNA results to be sure...upload to Gedmatch.com for that). It's just too early to tell the exact relationship. Getting your mom's DNA would help. Ultimately though, it's up to the paper trail.

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  • Thank you so much! I do have my mother's DNA results. She shares between 82, 74 & 90 cM with these cousins. Yes, one of their grandparents are siblings and they are indeed, 2nd cousins, per census records and family history. This great grandmother of mine is unknown and I believe comes from this family. I'll keep on investigating. Thanks again for your response and guidance.
    – Mary Ann
    Apr 17, 2019 at 4:59

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