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 >>>>>>>>>>> From: KATHRYN JOHNSTON <kathryn.johnston@sbcglobal.net> Subject: Re: [AUTOSOMAL-DNA] Finding shared atDNA ancestry without phasing Date: Mon, 18 Nov 2013 12:25:57 -0800 (PST) References: <1384723033.27753.YahooMailNeo@web184301.mail.ne1.yahoo.com><A590520F-F10A-43DA-9F6D-C169A62FBD43@verizon.net> In-Reply-To: <A590520F-F10A-43DA-9F6D-C169A62FBD43@verizon.net> Re: [AUTOSOMAL-DNA] Finding shared atDNA ancestry without phasing Hi Peter, Jim and Steven, I remember that Peter runs a Bahamas project which represents an isolated group of people and Steven has a lot of cousins marrying cousins too so both of you share something in common, endogamy and consanguinity. That is even more reason to consider the possibility that three people can all share with each other and they do not all have to share that match with the same ancestor. There can be more than one ancestral line represented among three people. Yes, phasing is necessary in this situation. And yes, it is very rare but if you are isolated on an island, it may not be that rare. Two copies of chromosome 4 does not mean exact copies. These can come from two different lines. Three people have 6 chromosomes total on chromosome 4. But each person carries two possible haplotypes. They could all carry "A" so match the same ancestor which is usually the case. However, they can carry any combination of A, B and C and not all match exactly the same ancestor but they still COULD match each other on one of the segments that are side by side. The computer program cannot distinguish one segment from another so it just reports it as a match. Alfred may carry haplotype segments A and B Betty may carry haplotype segments B and C Charles may carry haplotype segments A and C The software reads each one as a half-identical-region. The computer does not read which segment you have in common. But this scenario occurs only when each person has some combination of A, B and C. If a new person comes along with D plus A, B or C, then he will not match somebody but will match two out of the three people above. Regards, Kathy