Dear Dwight, I will respond to your questions in the order you have them in your message as follows: 1. Yes. It is definitely helpful, but not conclusive. You need to keep in mind that our autosomal DNA is made up of fragments from many different ancestors and that there is still a possibility that two people can match someone else on the same location, have the same number of SNPs in the HIR, have the same start and stop locations and yet still be matching on opposite chromosomes. 2. GEDmatch can't answer the question if only un-phased data has been uploaded to GEDmatch. However, using phased data would be helpful and comparisons of the phased data files would be informative. As you know, I am a great fan of the use of phased data in GEDmatch or elsewhere. Ideally, everyone should be uploading phased data to GEDmatch. However, many people don't have the skills or knowledge to deal with creating phased data. I am extremely careful when I am doing chromosome mapping that I don't make the assumption that if a person shares more than one IBD segment with me that the additional IBD segments came from the same ancestor that the first IBD segment came from. I have found too many situations where IBD segments came from different ancestors, particularly in situations such as my dad's where he comes from an endogamous population (Low German Mennonites). Each segment of your DNA that you are mapping should be tracked independently of other segments that you are mapping. Be very careful when you are analyzing smaller HIRs (particularly HIRs less than 5 cMs), since a large percentage of such HIRs will be IBS. Sincerely, Tim Janzen -----Original Message----- From: autosomal-dna-bounces@rootsweb.com [mailto:autosomal-dna-bounces@rootsweb.com] On Behalf Of Dwight Holmes Sent: Wednesday, December 18, 2013 9:56 AM To: autosomal-dna@rootsweb.com Subject: Re: [AUTOSOMAL-DNA] Family Tree DNA matches Tim - Thanks, as always, for your thoughtful, informative responses. I'd like to ask a couple of questions for my own benefit, and I'll assume others may also benefit from this (including Bob, whose thread this is!) 1. I know that segment start and stop points are approximations. But does the fact that the two segments have the exact same reported start and stop points, cM, and SNPs, add to the likelihood they are the same DNA segment? 2. As to the question of whether these are on the same or opposite sides of Ch 3, am I right that Gedmatch cannot answer that question directly? But that you might see in the data for the four people other evidence (a large number of smaller shared segments, for example) that might point to them all being related, or (in the absence of such supporting indications) not? Thanks! Dwight