23cM 1 Segment but two possible ancestral lines

[smudwhisk]

If the DNA match is across one segment is it only going to match one particular ancestral line or could if they coincidentally inherit sufficient on both sides of the chromosome it would show? 

I ask because Dad has a match with someone with 23cM across 1 segment yet they share two separate unrelated (apart from when later generations marry separately) ancestral lines.  In both Dad's and the matches' case, one is on their father's side and one on their mother's side.  I appreciate that without a chromosome browser on Ancestry and the other party hasn't uploaded elsewhere, its difficult to know for certain.

For Dad, the father's side is a 2xGGF but the matches is 4xGGF and on Dad's mother's side it is his 4xGGF and the matches' 5xGGF.  I'm assuming, perhaps wrongly, that it's likely to be on the paternal side as that is much closer generational level to Dad. 

Of the mutual 4-6th cousin shared matches with this person, 3 are confirmed on Dad's paternal side and 1 on the maternal side.  The mutual maternal side match matches a number of Dad's other maternal matches on that line but only this other person with an apparent overlap on both sides of Dad's family at 4-6th cousin level anyway.

I know there are two sides to each chromosome, would anyone have any views on whether it could just be that they both inherit sufficient DNA on that chromosome from both sides for it to show as that amount across 1 segment please on Ancestry?

I hope this makes sense, I have revised it a few times.

[avm228]

Not two sides, but two copies of each chromosome.

On the facts you have given it does seem possible that matching DNA has been inherited on both the maternal and paternal copies of the relevant chromosome. As you say, you’d need chromosome browser analysis to understand the match fully.

[smudwhisk]

Thanks avm, the more I look into it, the more I think that is the case.

Even though they are two separate copies of the same chromosome, it would still show as only one segment then?

I wish Ancestry would show 5-8th cousin shared matches, there could well be some other similar matches at lower level as there are quite a few matches on both those lines.