My sister, daughter and I all took DNA tests for fun. My sister and I show up on Ancestry as "close family," and share 1864 Centimorgans, and we do not share any relatives that my daughter and I share on one my father's side of the family.

I wonder whether she may be only a half sibling?

I am hesitant to ask to see her matches, and my other siblings are dead.

Any ideas how to pursue?


2 Answers 2


The Shared cM Project 3.0 tool v4 for 1,864cm suggests that by far the most likely options are:

  • Grandparent / Grandchild
  • Aunt / Uncle / Niece / Nephew
  • Half Sibling

with near zero probability for:

  • Great-Aunt / Great-Uncle / Great-Niece / Great-Nephew

If you are confident that your sister is of the same generation as you, then I think the above suggests that you may be half-sisters rather than full-sisters.

I recommend extreme sensitivity about asking to see her matches.

  • 1
    Thanks. May not do anything. I love her for who she is, and wouldn't upset her unless she brings it up.
    – ejohns48
    Commented Jul 14, 2019 at 13:09

Since you tagged with ancestry.com, I will assume that you and our sister tested through Ancestry, and suggest that you look at the DNA matches SHARED between you and your sister. While not definitive, significant inconsistencies (particularly closer than 2 or three cousin levels) might provide clues.

That listing (available to you) will not tell you what her cm match is with each person, only she can look that up.

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