Ann, I understand that a small error rate is tolerated. This is common in almost all industries. The point I'm trying to understand is how do we get a 7.7cM string (maybe 8 million ACTGs) that is identical (99.99%) to another 7.7cM string, and have that be IBS (or, to a genealogist like me, random)? But if that's the way biology works, why does FTDNA make 7.7cM the cutoff, if so many of the matches at that level are IBS? I need to be careful here, because I don't want FTNDA to increase the cutoff - I've found too many cousins in the 7-10cM range (it remains to be determined whether their large segments are IBD or IBS). Actually I 'd like a selection feature at FTDNA that would allow me to lower the cutoff to, say, 5cM (and see the additional matches at that level). I have cousins who have taken FF and don't show up as a match to me - I'd really like to be able to compare them using the Chromosome Browser to see what atDNA we have in common. I guess I need to talk them into joining me at GEDmatch... Jim Bartlett On 01/07/12, Ann Turner<[email protected]> wrote: 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 <[1][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 > ______________________________ For answers to Frequently Asked Questions about mailing lists, please see: [2]http://dgmweb.net/MailingListFAQs.html ------------------------------- To unsubscribe from the list, please send an email to A[3][email protected] with the word 'unsubscribe' without the quotes in the subject and the body of the message References 1. mailto:[email protected] 2. http://dgmweb.net/MailingListFAQs.html 3. mailto:[email protected]