Yes, the matches you see at FTDNA and23andMe must have at least one long segment, and the great majority (but not 100%) should be IBD. The issue comes up more with people using 3rd party tools, like GEDmatch, where you can set the threshold lower. The important thing is just to keep an open mind about your conclusions. This applies to the segments where you have found a paper connection, too. The match is not *necessarily* through the line you identified, particularly when you get to the 4th cousin level or so. As a side note, 23andMe will display 5 cM relatives in Relative Finder if you are sharing genomes. The theory is that you invited someone to share because you have some "prior knowledge" that would tilt the odds in your favor. I suspect that worked out well in the case of my husband, who received his first close match in the Turner Y-DNA project after many years. The other fellow had also tested at 23andMe, and by sharing genomes, we could see a 6 cM segment in common. I'm inclined to think that falls in the pool of true positives. Ann On Thu, Nov 17, 2011 at 5:39 AM, Jim Bartlett <[email protected]>wrote: > Thanks for this, Ann, > > You can see down to 1cM segments at FTDNA, but when you contact a match, > looking to find a Common Ancestor, all of the FTDNA, and 23&Me, matches > have at least one segment that is 7cM long or more. Restricting myself to > FF and RF, I can't contact someone with only a 5cM long segment. > > I thought the 7cM and 7.7cM segments were selected because of the very > high probability that they were IBD, and that the matches would indeed be > cousins, having a Common Ancestor from whom we both got that segment. > Please let me know if I've missed the fundamental concept here. >

23andMe will also show X choromosome matches less than 5 cM. I think 3 cM might be the cutoff. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Ann Turner Sent: Thursday, November 17, 2011 10:52 AM To: [email protected] Subject: Re: [AUTOSOMAL-DNA] Numbers differences between FTDNA and 23 & me Yes, the matches you see at FTDNA and23andMe must have at least one long segment, and the great majority (but not 100%) should be IBD. The issue comes up more with people using 3rd party tools, like GEDmatch, where you can set the threshold lower. The important thing is just to keep an open mind about your conclusions. This applies to the segments where you have found a paper connection, too. The match is not *necessarily* through the line you identified, particularly when you get to the 4th cousin level or so. As a side note, 23andMe will display 5 cM relatives in Relative Finder if you are sharing genomes. The theory is that you invited someone to share because you have some "prior knowledge" that would tilt the odds in your favor. I suspect that worked out well in the case of my husband, who received his first close match in the Turner Y-DNA project after many years. The other fellow had also tested at 23andMe, and by sharing genomes, we could see a 6 cM segment in common. I'm inclined to think that falls in the pool of true positives. Ann

There are gender specific differences in their X share algorithm (i.e. male vs male, male vs female, female vs female) On Thu, Nov 17, 2011 at 11:09 AM, Max Heffler <[email protected]> wrote: > 23andMe will also show X choromosome matches less than 5 cM. I think 3 cM > might be the cutoff. > > --