Well I think I understand what Ann, Dwight and Larry are trying to pour into my head. I guess an analogy of two superimposed pictures (xrays) works for me - and then a match would come up with any combination. But I thought that was the whole point of insisting on long segments. What I'm understanding is that the matching algorithm can scoot along and match with either one of two at each point along the whole string. I can see where this would be kind of murky in the short haul, but over a long segment, it still seems pretty amazing to get matches with folks that then don't match each other. I guess I could mark it up to statistics - like flipping heads 10 times in a row, or something. I had thought the explanation would be more like an anomoly, or lack of preciseness, in the read of the data... In other words, if I got 2 FFI tests would they be identical? I compared my FFA segments to the FFI segments and many weren't even close. So I came to the conclusion that the "picture" the FFI test takes is a little fuzzy, and not a real precise observation. But it appears to be roughly right - as a genealogist, I'm still working with my matches and finding Common Ancestors. I'm not sure if we do in fact share the large atDNA segment with each other, but I am sure that we've come to the same conclusions on the paper trails. I'm hopeful that as more and more folks take this test, and maybe as the 23&me results are added in, we will begin to build a body of info that will help us sort it all out. Thanks again for 'splaining this to an engineer;>j Jim Bartlett On 01/06/12, Ann Turner<[email protected]> wrote: It could be a sign that some of those segments are Identical by State. As noted by others in this thread, we're looking at genotypes, where we don't know which allele came from each parent. If you could split the genotypes into their two haplotypes, this would clarify the picture. That generally takes father/mother/child trio data, though. For the initial query in this thread, pair-wise comparisons of everyone with everyone else is a reasonable first pass at deciding whether the segment comes from a single common ancestor. Ann Turner On Fri, Jan 6, 2012 at 1:46 PM, Jim Bartlett <[email protected]>wrote: > And yes, when I emailed this info to each group, some did confirm that > although they matched me as noted, they didn't match one or more of the > others in the same way. I find this very puzzling - that two folks can > have > the same long segment of DNA that is an exact match with me, and yet they > don't see such a match when they look at each other. Can anyone explain > to > my engineer brain why this is so? [to me this is like two lines each > being > parallel with a third line but not being parallel with each other... > QEnot] > ______________________________ For answers to Frequently Asked Questions about mailing lists, please see: http://dgmweb.net/MailingListFAQs.html ------------------------------- To unsubscribe from the list, please send an email to [email protected] with the word 'unsubscribe' without the quotes in the subject and the body of the message

If you got 2 FFI tests, the raw data would "only" be 99.99% identical. There will be a few genotyping errors, but FTDNA (and 23andMe) will tolerate a single mismatch that's embedded in a long consecutive run of matching SNPs. The problem with the Affy chip was that the error rate was somewhat higher, and FTDNA had to tolerate too many mismatches, giving rise to more false positives. Ann On Fri, Jan 6, 2012 at 3:25 PM, Jim Bartlett <[email protected]>wrote: > Well I think I understand what Ann, Dwight and Larry are trying to pour > into my head. I guess an analogy of two superimposed pictures (xrays) works > for me - and then a match would come up with any combination. But I thought > that was the whole point of insisting on long segments. What I'm > understanding is that the matching algorithm can scoot along and match with > either one of two at each point along the whole string. I can see where > this would be kind of murky in the short haul, but over a long segment, it > still seems pretty amazing to get matches with folks that then don't match > each other. I guess I could mark it up to statistics - like flipping heads > 10 times in a row, or something. > > I had thought the explanation would be more like an anomoly, or lack of > preciseness, in the read of the data... In other words, if I got 2 FFI > tests would they be identical? I compared my FFA segments to the FFI > segments and many weren't even close. So I came to the conclusion that the > "picture" the FFI test takes is a little fuzzy, and not a real precise > observation. > > But it appears to be roughly right - as a genealogist, I'm still working > with my matches and finding Common Ancestors. I'm not sure if we do in fact > share the large atDNA segment with each other, but I am sure that we've > come to the same conclusions on the paper trails. I'm hopeful that as more > and more folks take this test, and maybe as the 23&me results are added in, > we will begin to build a body of info that will help us sort it all out. > > Thanks again for 'splaining this to an engineer;>j > Jim Bartlett >