My dad, his nephew and three grand-daughters all have their DNA on Ancestry (mine is on FtDNA alas). They have dozens of matches on Dads FF side and distant MM side, but few on his MF side.
I deleted all the Ancestry groups I'd made, in Dads profile and called up the matches shared by Dad and his nephew and marked them with one group and did the same with each of his grand-daughters. This showed me that all Dad's second cousins on the FF side match with all 5 of them. 3rd cousins and further out match with some but rarely all. I have yet to work out if there are any patterns, but further down the tree (if you get my meaning) the matches are less (and maybe just Dad and one other).
I also did the same for my girls tests, which shows where their paternal and maternal matches are.
Then I picked one of Dad's known maternal matches and made a group of their common matches. I tried to do this with each different common ancestor. I still have no idea who some people are, and how they fit into the tree but they match with Dad and someone else. His MM family and further back have a great bunch of matches, but there are less than 10 on his MF lines.
One match matched a bunch of others on his MMFM line, and was in Canada but all the others are in Australia. This person had no tree. So I went back to my family tree and chased down the tree in 4gggf's brother, and lo, one of his gg grandsons went off to Canada. I had only built the family tree down to his g grandsons, thinking I was getting to far away from my main tree.
This method brought up some matches I had not already identified but still leaves a large pool of matches, even over 20cMs, who have no trees and I have no idea beyond they match with Dad and one other person.
Some of the matches with Dad who showed up when we first tested have now put up or updated their family tree, or match with someone else who has a tree, so it pays to re-check them occasionally.
Does this help at all, or just make you more confused? It did my head in for a time.
Di
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