tag:blogger.com,1999:blog-270065650508943132.post2766039124611930032..comments2017-08-16T01:57:49.284-07:00Comments on Not just the PARRYs – a genealogy blog for all my ancestors.: Autosomal DNA Discussions - and some statistics for my kitsBarbara Griffithshttp://www.blogger.com/profile/06663134740555588042noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-270065650508943132.post-56277748761003321832017-08-13T17:37:25.559-07:002017-08-13T17:37:25.559-07:00Barbara, Yes that's my experience too. All the...Barbara, Yes that's my experience too. All the scientific papers tell us that the more frequent a haplotype is the less likely it is to be recent. It takes a long time for selection to take effect, and for a haplotype to reach a high frequency in a population. I don't know how the new GSA chip, used by both 23andMe and Living DNA, is going to work. It would be good if it could provide better coverage in some of the SNP-poor and pile-up-prone regions.Debbie Kennetthttps://www.blogger.com/profile/11573470282571579765noreply@blogger.comtag:blogger.com,1999:blog-270065650508943132.post-54888967147219377152017-08-13T05:25:38.767-07:002017-08-13T05:25:38.767-07:00Thanks, Debbie. That is a good question - one of ...Thanks, Debbie. That is a good question - one of the things I noticed when I identified my first shared ancestor with a DNA match (a 4c1r) was that they were the only person matching me over that segment. (It was particularly interesting as, at that time, I was working on looking for TGs!) I'll go through all the connections and let you know what patterns there are. Regarding the pile-up on chromosome 15, yes, I agree. I'll check my data from the other companies, to see how that area compares on their tests (although I think some of them use the same chip, anyway). Do you know whether the new 23andMe test will have better coverage in that area?Barbara Griffithshttps://www.blogger.com/profile/06663134740555588042noreply@blogger.comtag:blogger.com,1999:blog-270065650508943132.post-34074480442594791952017-08-12T06:18:39.556-07:002017-08-12T06:18:39.556-07:00Barbara, I'd be interested to know about the p...Barbara, I'd be interested to know about the pattern of matching where you've found connections on the smaller segments. Were this single pairwise matches between you and your cousin or did you find other people matching on the same segment. You make a good point about the number of SNPs in the segment. I was intrigued by your big pile-up on chromosome 15. I wonder if that area would still be a match if there the SNP density was higher in that area on a different chip.Debbie Kennetthttps://www.blogger.com/profile/11573470282571579765noreply@blogger.comtag:blogger.com,1999:blog-270065650508943132.post-82981796145133477282017-08-10T01:39:41.717-07:002017-08-10T01:39:41.717-07:00Thank you for your comment, Louis, that's much...Thank you for your comment, Louis, that's much appreciated.<br /><br />Yes, that makes sense - I think you've summed it up well. Some small segments can be relevant, as I showed in my post at https://notjusttheparrys.blogspot.co.uk/2017/06/ where a 6.9cM segment I have triangulates with my father's siblings (and has to be genuine for the visual phasing to work). But just because a segment triangulates, it doesn't necessarily make it genealogically relevant, even for the longer segments. There's still a lot we don't know!<br />Kind regards<br />BarbaraBarbara Griffithshttps://www.blogger.com/profile/06663134740555588042noreply@blogger.comtag:blogger.com,1999:blog-270065650508943132.post-31459316891154172002017-08-09T18:52:14.115-07:002017-08-09T18:52:14.115-07:00Another excellent article. Keep them coming!
You&...Another excellent article. Keep them coming!<br /><br />You've covered most of it. The general rules are when single matching, you likely need a 15 cM to be likely IBD. If you triangulate, Jim Bartlett is sure that you only need 7 cM (possibly even 5 cM) and you're likely IBD. <br /><br />The trouble with the shorter segments is that they're generally not genealogically relevant, and may originate 10 generations or 20 generations back or even longer. There are of course exceptions, and you're parent may have had a 30 cM match that got chopped to 5 cM in you when it got chopped by a crossover the other 25 cM got your other grandparent's chromosome instead.<br /><br />The key point is that for a segment to be IBD, it must triangulate. The opposite is not true. A triangulated segment is not necessarily IBD. Chance matches can happen on shorter IBD segments. But by using triangulated segments, you are eliminating a lot of false matched that are guaranteed to not be IBD.<br /><br />I hope that makes sense.<br />Louis Kesslerhttps://www.blogger.com/profile/11704667321407909489noreply@blogger.com