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DNA Match Question

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gmcoates
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DNA Match Question

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Hello !

I have a DNA match as follows;
Shared DNA: 163 cM across 6 segments
My half brother has the same match but as follows;
Shared DNA: 56 cM across 4 segments

What am I to deduce from this ?

To find my relationship with the match, I should use...
o Higher figure
o Lower figure
o Average
o Something else ?
ericdubois
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I would start with the smaller value as a safer assumption, which would make your match somewhere between 3rd and 4th cousin in the branch you share with your half brother. So common ancestor at the 5th or 6th generation.

As for the additional shared DNA between you and your match, it could be:
1. that you inherited segments from the same ancestor, which your match also inherited but not your half brother.
2. that you and your match share an IBP segment (Identical by population).
3. that you also match via your other parent.
gmcoates
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Thanks for the reply, that makes sense

1 I was hoping for and would let me assume the full 163cm, I can see now that is not a safe assumption
2 The match is just chance and in effect "noise"
3 I think I understand. We have different mothers. My mother matches and his doesn't, so I get a contribution he doesn't

I guess I can't know what to choose, so your recommendation makes sense, thanks

Mark
ericdubois
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I didn't rule out the possibility that the full 163cM came from the same ancestor. But that by looking further back, you'll have a better chance of finding a common ancestor. But the common ancestor could be at the 4th generation or at the 7th. We're dealing with probability here, not certainty.

If your mother matches that individual and your half brother on your father's side also matches the same individual, then you would have 2 ancestors in common with that individual. One on your father's side and one on your mother's.

Eric
gmcoates
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Thanks Eric
The issue here is that it is probably a match with my unknown paternal grandfather !

So I can't find a match, unless I can find commonalities in multiple trees.
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