I have a segment on chromosome pair 17 where I triangulate with genetic cousins 'John' and 'Jane'. I also share a portion of the same segment with my known half first cousin, 'Sara'. Sara and I share the same patrilineal grandfather but not grandmothers. Neither John nor Jane share any DNA with Sara. Can I eliminate my patrilineal grandfather and his ancestors as the potential source of my shared ancestry with John and Jane? Here's the 23andMe results: Jane / Me 17 71,000,000-77,000,000 18.6cM 1,527 SNPs John / Me 17 72,000,000-77,000,000 21.6cM 1,324 SNPs Jane / John 17 72,000,000-81,000,000 21.6cM 1,854 SNPs Sara / Me 17 64,000,000-77,000,000 32.1cM 3,263 SNPs Sara / John None Sara /Jane None

Dear Mardon, The HIRs are all relatively long and all contain a fairly large number of SNPs. It is therefore reasonable to assume that they are IBD. Based on the information you presented you should map the segment you share with John and Jane to your mother and you should look for shared ancestors with them in your mother's family tree. Map the segment you share with Sara to your paternal grandfather. Sincerely, Tim Janzen -----Original Message----- From: genealogy-dna-bounces@rootsweb.com [mailto:genealogy-dna-bounces@rootsweb.com] On Behalf Of Mardon via Sent: Sunday, October 4, 2015 12:15 PM To: GENEALOGY-DNA-L@rootsweb.com Subject: [DNA] Triangulation for Eliminating Part of a Tree? I have a segment on chromosome pair 17 where I triangulate with genetic cousins 'John' and 'Jane'. I also share a portion of the same segment with my known half first cousin, 'Sara'. Sara and I share the same patrilineal grandfather but not grandmothers. Neither John nor Jane share any DNA with Sara. Can I eliminate my patrilineal grandfather and his ancestors as the potential source of my shared ancestry with John and Jane? Here's the 23andMe results: Jane / Me 17 71,000,000-77,000,000 18.6cM 1,527 SNPs John / Me 17 72,000,000-77,000,000 21.6cM 1,324 SNPs Jane / John 17 72,000,000-81,000,000 21.6cM 1,854 SNPs Sara / Me 17 64,000,000-77,000,000 32.1cM 3,263 SNPs Sara / John None Sara /Jane None

The partial overlap is only 5Mbp. So that may be the reason for the non-match. You should determine TGs with John & Jane and with Sara. And/or upload to GEDmatch where you can compare Sara to others with a smaller threshold. Otherwise you could make the assumption you did, and be ready to change it, if warranted. Jim - www.segmentology.org > On Oct 4, 2015, at 3:14 PM, Mardon via <genealogy-dna@rootsweb.com> wrote: > > I have a segment on chromosome pair 17 where I triangulate with genetic > cousins 'John' and 'Jane'. I also share a portion of the same segment with > my known half first cousin, 'Sara'. Sara and I share the same patrilineal > grandfather but not grandmothers. Neither John nor Jane share any DNA with > Sara. Can I eliminate my patrilineal grandfather and his ancestors as the > potential source of my shared ancestry with John and Jane? > > Here's the 23andMe results: > > Jane / Me 17 71,000,000-77,000,000 18.6cM 1,527 SNPs > John / Me 17 72,000,000-77,000,000 21.6cM 1,324 SNPs > Jane / John 17 72,000,000-81,000,000 21.6cM 1,854 SNPs > Sara / Me 17 64,000,000-77,000,000 32.1cM 3,263 SNPs > Sara / John None > Sara /Jane None > >

Dear Jim, The length of the segment where John and Jane match with Mardon but don't match with Sara is at least 18 cMs and this segment contains at least 1300 SNPs. Partial overlap should not be a factor here. It is very highly probable that Jane and John are matching Mardon on one chromosome and that Sara is matching Mardon on the opposite chromosome. Additional triangulation with other people would be fine, but it won't change the fact that the genetic data strongly suggests that Jane and John are matching Mardon on one chromosome and that Sara is matching Mardon on the opposite chromosome. Sincerely, Tim Janzen -----Original Message----- From: genealogy-dna-bounces@rootsweb.com [mailto:genealogy-dna-bounces@rootsweb.com] On Behalf Of Jim Bartlett via Sent: Sunday, October 4, 2015 1:27 PM To: Mardon; genealogy-dna@rootsweb.com Subject: Re: [DNA] Triangulation for Eliminating Part of a Tree? The partial overlap is only 5Mbp. So that may be the reason for the non-match. You should determine TGs with John & Jane and with Sara. And/or upload to GEDmatch where you can compare Sara to others with a smaller threshold. Otherwise you could make the assumption you did, and be ready to change it, if warranted. Jim - www.segmentology.org