You are correct about the biological reality. Segments do not jump back and forth. However, the DNA results (e.g. CT) you receive for a particular SNP are a "genotype." The DNA is chopped into tiny pieces before analysis, which uses probes to detect the presence of a particular allele. The only thing we can tell is that a C is present in some pieces and a T is present in other pieces. Computer algorithms attempt to predict which SNPs are traveling together as a package on a single chromosome (a haplotype) but they don't always get it right. Ann Turner On Thu, Jan 7, 2016 at 7:23 AM, Patti Easton <amharach@msn.com> wrote: > Ann, > > I really appreciated this article. I watch this list as an eager novice, > knowing I have a steep learning curve, and having gained much knowledge > from > the talented people who contribute here. Hopefully this is appropriate to > ask here, again given my novice status. > > What I have trouble wrapping my head around in this article, particularly > given the DNA doesn't lie, DNA is a fact and end all, be all, is how does > Germline allow matches to jump back and forth between segments? Isn't this > counter intuitive to something directed at extracting genetic code? And > without asking too much of the scientific end, how is that even possible. > How can DNA move to other sections? > > Perhaps DNA isn't as black and white as I have been led to view it. I > don't > see it as fluid. But while coding appears to not fluctuate, I guess I am > seeing that perhaps the testing makes it so. > > Thank you! > Regards, > Patti Easton > > > > > -----Original Message----- > From: genealogy-dna-bounces@rootsweb.com > [mailto:genealogy-dna-bounces@rootsweb.com] On Behalf Of Ann Turner via > Sent: Wednesday, January 6, 2016 8:05 PM > To: DNA Genealogy Mailing List <GENEALOGY-DNA@rootsweb.com> > Subject: [DNA] segments and cM at AncestryDNA > > This blog post explains some of the questions we've raised about the number > of shared cM and segments at AncestryDNA and how they compare to numbers > seen at GEDmatch, 23andMe, and FTDNA. > > > http://blogs.ancestry.com/techroots/behind-the-new-ancestrydna-feature-amoun > t-of-shared-dna/ > > Ann Turner > > ------------------------------- > To unsubscribe from the list, please send an email to > GENEALOGY-DNA-request@rootsweb.com with the word 'unsubscribe' without the > quotes in the subject and the body of the message >

Thank you for the reply Ann. So when looking at results from Ancestry uploaded to gedmatch, does that mean that the chromosome browser comparisons would be faulty? How much error should one expect? Is this just minutia, or would it factor into comparisons? Is this why Ancestry has no chromosome browser? Thank you again, Patti -----Original Message----- From: genealogy-dna-bounces@rootsweb.com [mailto:genealogy-dna-bounces@rootsweb.com] On Behalf Of Ann Turner via Sent: Thursday, January 7, 2016 5:51 AM Cc: DNA Genealogy Mailing List <genealogy-dna@rootsweb.com> Subject: Re: [DNA] segments and cM at AncestryDNA You are correct about the biological reality. Segments do not jump back and forth. However, the DNA results (e.g. CT) you receive for a particular SNP are a "genotype." The DNA is chopped into tiny pieces before analysis, which uses probes to detect the presence of a particular allele. The only thing we can tell is that a C is present in some pieces and a T is present in other pieces. Computer algorithms attempt to predict which SNPs are traveling together as a package on a single chromosome (a haplotype) but they don't always get it right. Ann Turner On Thu, Jan 7, 2016 at 7:23 AM, Patti Easton <amharach@msn.com> wrote: > Ann, > > I really appreciated this article. I watch this list as an eager > novice, knowing I have a steep learning curve, and having gained much > knowledge from the talented people who contribute here. Hopefully > this is appropriate to ask here, again given my novice status. > > What I have trouble wrapping my head around in this article, > particularly given the DNA doesn't lie, DNA is a fact and end all, be > all, is how does Germline allow matches to jump back and forth between > segments? Isn't this counter intuitive to something directed at > extracting genetic code? And without asking too much of the scientific end, how is that even possible. > How can DNA move to other sections? > > Perhaps DNA isn't as black and white as I have been led to view it. I > don't see it as fluid. But while coding appears to not fluctuate, I > guess I am seeing that perhaps the testing makes it so. > > Thank you! > Regards, > Patti Easton > > > > > -----Original Message----- > From: genealogy-dna-bounces@rootsweb.com > [mailto:genealogy-dna-bounces@rootsweb.com] On Behalf Of Ann Turner > via > Sent: Wednesday, January 6, 2016 8:05 PM > To: DNA Genealogy Mailing List <GENEALOGY-DNA@rootsweb.com> > Subject: [DNA] segments and cM at AncestryDNA > > This blog post explains some of the questions we've raised about the > number of shared cM and segments at AncestryDNA and how they compare > to numbers seen at GEDmatch, 23andMe, and FTDNA. > > > http://blogs.ancestry.com/techroots/behind-the-new-ancestrydna-feature > -amoun > t-of-shared-dna/ > > Ann Turner > > ------------------------------- > To unsubscribe from the list, please send an email to > GENEALOGY-DNA-request@rootsweb.com with the word 'unsubscribe' without > the quotes in the subject and the body of the message > ------------------------------- To unsubscribe from the list, please send an email to GENEALOGY-DNA-request@rootsweb.com with the word 'unsubscribe' without the quotes in the subject and the body of the message

Patti GEDmatch uses a standard threshold of 700 SNPs (in a row) and 7cM. Close to the 7cM threshold, roughly half of the Matches may be false. Shared segments at 7cM will be true (IBD) over 90% of the time; at a minimum of 15cM virtually all shared segments are IBD. I am a proponent of Triangulation. I have found that most of the false segments above 7cM will not Triangulate, so this is a good way to cull most of them out. See my blog for several posts on Triangulation. I believe AncestryDNA does not have a browser for privacy reasons. But many of their customers are uploading to GEDmatch to use the genetic tools. Jim - www.segmentology.org > On Jan 7, 2016, at 8:33 AM, Patti Easton via <genealogy-dna@rootsweb.com> wrote: > > Thank you for the reply Ann. So when looking at results from Ancestry > uploaded to gedmatch, does that mean that the chromosome browser comparisons > would be faulty? How much error should one expect? Is this just minutia, > or would it factor into comparisons? Is this why Ancestry has no chromosome > browser? > > Thank you again, > Patti > >

Patti Another way I try to explain this is that the testing process gets a value for each of the 700,000 SNPs on your mother's side and your father's side - so actually 1,400,000 results in all. The process now have does not know which ones are maternal and which are paternal - it just knows there are two values for each SNP. The presumption is that for a long enough comparison (between you and a potential Match), the only way two long strings of SNPs could be identical is if they were from the same ancestor. I needed several different explanations of this process before the "lightbulb" came on for me. In my blog (in my tag line), an early post explained the difference between ancestral segments (what you have in your body - from ancestors) and shared segments (generated by computer algorithms looking at all the SNPs). When a shared segment matches an ancestral segment we say it is IBD (Identical By Descent); when the shared segment is not the same as an ancestral segment the shared segment is false, and we say it is not-IBD or it is IBS (Identical By State) or IBC (Identical By Chance) [different folks use different terms] Hope this helps. Jim - www.segmentology.org > On Jan 7, 2016, at 7:50 AM, Ann Turner via <genealogy-dna@rootsweb.com> wrote: > > You are correct about the biological reality. Segments do not jump back and > forth. However, the DNA results (e.g. CT) you receive for a particular SNP > are a "genotype." The DNA is chopped into tiny pieces before analysis, > which uses probes to detect the presence of a particular allele. The only > thing we can tell is that a C is present in some pieces and a T is present > in other pieces. Computer algorithms attempt to predict which SNPs are > traveling together as a package on a single chromosome (a haplotype) but > they don't always get it right. > > Ann Turner > >> On Thu, Jan 7, 2016 at 7:23 AM, Patti Easton <amharach@msn.com> wrote: >> >> Ann, >> >> I really appreciated this article. I watch this list as an eager novice, >> knowing I have a steep learning curve, and having gained much knowledge >> from >> the talented people who contribute here. Hopefully this is appropriate to >> ask here, again given my novice status. >> >> What I have trouble wrapping my head around in this article, particularly >> given the DNA doesn't lie, DNA is a fact and end all, be all, is how does >> Germline allow matches to jump back and forth between segments? Isn't this >> counter intuitive to something directed at extracting genetic code? And >> without asking too much of the scientific end, how is that even possible. >> How can DNA move to other sections? >> >> Perhaps DNA isn't as black and white as I have been led to view it. I >> don't >> see it as fluid. But while coding appears to not fluctuate, I guess I am >> seeing that perhaps the testing makes it so. >> >> Thank you! >> Regards, >> Patti Easton >> >> >> >> >> -----Original Message----- >> From: genealogy-dna-bounces@rootsweb.com >> [mailto:genealogy-dna-bounces@rootsweb.com] On Behalf Of Ann Turner via >> Sent: Wednesday, January 6, 2016 8:05 PM >> To: DNA Genealogy Mailing List <GENEALOGY-DNA@rootsweb.com> >> Subject: [DNA] segments and cM at AncestryDNA >> >> This blog post explains some of the questions we've raised about the number >> of shared cM and segments at AncestryDNA and how they compare to numbers >> seen at GEDmatch, 23andMe, and FTDNA. >> >> >> http://blogs.ancestry.com/techroots/behind-the-new-ancestrydna-feature-amoun >> t-of-shared-dna/ >> >> Ann Turner >> >> ------------------------------- >> To unsubscribe from the list, please send an email to >> GENEALOGY-DNA-request@rootsweb.com with the word 'unsubscribe' without the >> quotes in the subject and the body of the message > > ------------------------------- > To unsubscribe from the list, please send an email to GENEALOGY-DNA-request@rootsweb.com with the word 'unsubscribe' without the quotes in the subject and the body of the message