I don't think there has been a lot of phased studies. It is something that simply needs to be done. A four way match in an endogamous group could have: AB AB BC AC They all match each other but you should see fully identical matching for the first two. You would have to look at a chromosome browser that shows the fully identical (double-stranded) segments. This is one more reason to have these kinds of browsers made more readily available by the testing companies. This is the only situation that I can think of that would cause a complete four-way match. I think that if everyone matches everyone else and you have a robust match with all four people with no full matching, and no endogamy or consanguinity, then you are most likely dealing with a single lineage and not the above situation. But when dealing with a close-knit heavily drifted community, I would still be on the look-out for these rare birds. I have certainly heard of cases where ALMOST everybody matched everybody else. There could have been threshold issues, mutations, SNP poor regions, errors, IBS etc. instead of IBD endogamy but how would you know if you don't look at the phased raw data and pinned the segment on a specific ancestor? A situation where there are multiple matches, but not sharing with everyone might be: AD, AC, BC, AB, CD, BD. Each of the 6 people matches with four other people and does not match with one. It could fool you into believing that everyone comes from the same MRCA even though there are four ancestors that provided matching segments within the same two position numbers. We all know of groups of ancestors who were highly proliferative. It is extremely important to make sure that everyone matches everyone else as you say when dealing with 4 or more people. But with 3 people, there is no guarantee you have a single ancestral line (even if they do all match each other) without phasing them and/or clear identification of the line. People need to study this further in a real life situations. Right now we are only dealing with a hypothetical problem. Kathy ------ > Hello Kathy, > > What if the ancestry is NOT from an > endogamous group?  What if it is from an > endogamous group but is a 4 way match? - > Where all the matches are matching each other? > Thanks and sincerely, Peter