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How much DNA is shared with half siblings?

williammatthewread
male
Inlägg: 4
At Ancestry DNA I have a close match listed as a 1st cousin.
1121cm across 32 segments on my biological fathers side.
She doesn't know who her father is,and has no links to me on her mother's side.
She is linked to being closely related to both my biological aunts.
My biological father has only two sisters,that have had no children.
Is it possible that she is my half sister.
My biological father was pretty irresponsible the first half of his life,ang got around so to speak.

ericdubois
male
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According to this calculator, the shared cM is a bit low for half sibling, but not entirely impossible.

How did you figure it was on your father's side?

williammatthewread
male
Inlägg: 4
Her links all point to my biological fathers side,and closely to me and my aunt(bio fathers sister).
Neither of my bio fathers sisters had children,and he had no brothers.

williammatthewread
male
Inlägg: 4
My mother was adopted at 2yo in a closed adoption,and I have yet to find anyone even distantly related to her.
She divorced my biological father when I was 8mo old.
I never knew him or his family.
I did speak to one of his sisters about 10yrs ago.
She knew nothing about me even though her brother was married to my mother for over a year.
He was irresponsible and drifted around a lot the first half of his life.
The lady I mentioned in my first post is the only other close relation by DNA and linked to my aunt who recently had an Ancestry DNA test.
My aunt's numbers are 1647cm across 72 segments.

ericdubois
male
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Based on this information, I see 2 possibilities.
1. This lady is indeed your half sister.
2. Your grandfather was as promiscuous as your father and had another child no one knew about. It this case the lady would be your half first cousin or half aunt. Based on the numbers, the latter is the most probable scenario.
william-dna.png

williammatthewread
male
Inlägg: 4
Thank You!!
I guess it means more research on my part.
The Grandfather was a widower,and remarried.
I just figured the numbers would be lower,that far removed.

ericdubois
male
Volunteer moderator
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Visa deras familjeträd.
If this turns out to be true, you would actually be quite close biologically, since your match would be your half-aunt and your father's half-sister. Not as close as if she were your half sister, but the numbers made that an unlikely scenario.

In my limited experience, the relationship is usually on the far end of the range given by any calculator. So if a test says 2nd to 4th cousin, more often than not it will be a 4th cousin.

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