Single DNA segment - 28cM: Passed Unchanged Since 1600's.

[katerennie4]

I don't think it's that impossible.

My dad & I share a single 23cm segment with a woman, her brother, and her son. We know the connection is pre-1800 because of our trees. And even if the connection is just one more generation back from where my tree ends (or roughly to someone born circa 1760-1770), I'd be a 6th cousin to her/her son. And I doubt it's just one more back.

[sjadelson]

I don't think it's that impossible.

My dad & I share a single 23cm segment with a woman, her brother, and her son. We know the connection is pre-1800 because of our trees.

I have several of that size myself in that timeframe (200 years). However, your case is (roughly) half as many generations as the original question.

In the manner of all random and arbitrary events, it could happen, but I would think it very, very rare when a segment that large is passed for 400 years. The chance of it happening in a separate line as well in order to be comparable now seems astronomically small.

[katerennie4]

I have several of that size myself in that timeframe (200 years). However, your case is (roughly) half as many generations as the original question.

In the manner of all random and arbitrary events, it could happen, but I would think it very, very rare when a segment that large is passed for 400 years. The chance of it happening in a separate line as well in order to be comparable now seems astronomically small.

He did say they'd be 10th cousins though, and my "cousins" and I are at the very least 6th cousins, but more probably 7th+ cousins. I agree, they should explore every other line first, before they settle on this couple as the source of their shared DNA. Trees can be deceiving. My father & another man are likely (95% certainty) 6th cousins thru one Palatine German/English family. I was well beyond ready to declare this the source of the match, especially knowing that this person did not match my grandmother (the 6th cousin designation is thru my father's father) but then I was thrown a boulder when he came back and told me the relationship was thru his father and not his mother (the source of the 6th cousin match on his end). Needless to say I was crushed. I was left to chalk him up as another one of my unknown, likely forever, Irish relatives.

[Geneadict]

Agree with those who state highly unlikely and more likely originating with multiple ancestors or ancestor(s) not identified in pedigree, especially if complete pedigree for all ancestral lines for both individuals going back to the 1600s are not available.