If such lines are well documented, yes. In most cases they are not. Andreas > On 30 Sep 2017, at 02:05, Wjhonson <[email protected]> wrote: > > 20th cousins? > So you're saying it *is* possible to use atDNA to confirm lines into medieval times > > > > > > > > > -----Original Message----- > From: Tim Janzen <[email protected]> > To: genealogy-dna <[email protected]> > Sent: Thu, Sep 28, 2017 8:26 pm > Subject: Re: [DNA] Endogamy does exist in USA data > > Dear Belinda, > I have been emphasizing in my presentations for quite a few years that > trying to predict the precise genealogical connection between any two people > who share say 50 cMs or less with each other is fraught with problems. I > try to emphasize that the relationship could be as close as 2nd cousins or > could be as distant as 20th cousins. You can improve the predictions if you > start using cousin clusters to generate the prediction for the genealogical > relationships. However, none of the companies are doing that yet. We need > to see the companies automate chromosome mapping, but that hasn't happened > yet either. > Sincerely, > Tim > > -----Original Message----- > From: GENEALOGY-DNA [mailto:[email protected]] On Behalf Of > Belinda Dettmann > Sent: Thursday, September 28, 2017 5:19 PM > To: [email protected] > Subject: Re: [DNA] Endogamy does exist in USA data > > Thanks for that, Tim. The degree of endogamy becomes important in the > context of predicting relationships. Examples are in the statistics and > guidelines given in references such as ISOGG where values only apply to > populations with a degree of endogamy similar to that found in the USA. As a > practical guide, the commonly used predictions (at FTDNA, 23andMe and > ancestry.com) for known relationships from third cousin outward are not > correct for ancestry which comes from mixtures of populations with less > inbreeding than in the USA overall. > As an Australian with mixed ancestry from 8 different regions of the British > Isles, plus Germany and Poland, I have thousands of DNA matches, for which, > for third cousins and worse, the predictions are all wrong. The > relationships are much more distant than predicted and most links are > impossible to find. Ranges usually cover the right value, but the actual > predictions are rubbish. Similar situations apply for testers who live in > the British isles, or South Africa, or New Zealand, or Poland, to my certain > knowledge. > We all find it disconcerting when told how close our middle-distance matches > should be, when we know they are nothing of the kind. > I agree that chromosome mapping is essential in doubtful situations, and I > routinely download DNA for my known relatives to Gedmatch for that purpose, > if they agree. There again, the guidelines for length of segments need some > adjustments, as I find that fewer long and more short segments are the order > of the day for known cousins of third degree or more in testers from mixed > populations. > > > > ------------------------------- > 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 > > > ------------------------------- > 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

This needs more discussion. There is a big difference between a shared 7cM segment coming from an ancestor 20 generations ago - a real possibility; and some specific ancestor 20 generations ago being the one who passed down that segment - an extremely low probability. Some ancestor 20 generations ago may be true, but which one requires a LOT more evidence that just two very deep Trees which include the same ancestor. atDNA will "work" well beyond 4C, determining the Common Ancestor is much harder. Jim Bartlett - atDNA blog: www.segmentology.org > On Sep 29, 2017, at 7:00 PM, Andreas West <[email protected]> wrote: > > If such lines are well documented, yes. In most cases they are not. > > Andreas > >> On 30 Sep 2017, at 02:05, Wjhonson <[email protected]> wrote: >> >> 20th cousins? >> So you're saying it *is* possible to use atDNA to confirm lines into medieval times >>

My point was that it is impossible to accurately predict the genealogical relationship for someone who shares between say 5 cMs and say 50 cMs with you based solely on a one-to-one comparison. Those genealogical connections could be as far back as 20th cousins or even further back. We can come up with average predicted relationships for each cM total, but at the end of the day we are still simply left with a range of possible relationships. As I mentioned in my last message, you can improve your predictions if you use clusters of cousins for the comparisons. At some point we may be able to accurately map some segments back as many as 12 to 15 generations. I think that getting to 20 generations is going to be nearly impossible due to the lack of genealogical records for most people more than about 10 to 15 generations back. Mapping segments to ancestors who lived 7 to 10 generations back is possible now. Tim -----Original Message----- From: GENEALOGY-DNA [mailto:[email protected]] On Behalf Of Andreas West Sent: Friday, September 29, 2017 4:01 PM To: [email protected] Subject: Re: [DNA] Endogamy does exist in USA data If such lines are well documented, yes. In most cases they are not. Andreas > On 30 Sep 2017, at 02:05, Wjhonson <[email protected]> wrote: > > 20th cousins? > So you're saying it *is* possible to use atDNA to confirm lines into medieval times