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 --------------- 
> From: peterebay@yahoo.com 
> Subject: Re: [AUTOSOMAL-DNA] Finding shared > atDNA ancestry without phasing 
> Date: Mon, 18 Nov 2013 13:20:34 -0500 > > Hello Steven, > > If Alfred matches Betty on a 7cM or > greater segment of chromosome 4 and Alfred > matches Charles on a 7cM or greater > segment of chromosome 4 (which overlaps > the Alfred/Betty segment) and Betty > matches Charles on this same >=7cM > segment, then I believe this almost > definitely confirms (or confirms) they all > received that segment from a shared > ancestor. No phasing is necessary. > > I understand they each have two copies of > chromosome 4. > > I would like to hear from anyone as to why > the above statement is wrong. > > Thank you and sincerely, Peter > > Peter J. Roberts