tag:blogger.com,1999:blog-5826248344207578284.post4254581156874458874..comments2024-03-03T11:33:31.376-05:00Comments on Family Sleuther: The Limits of TriangulationFamily Sleutherhttp://www.blogger.com/profile/11584864778317578299noreply@blogger.comBlogger9125tag:blogger.com,1999:blog-5826248344207578284.post-46008486199021958532019-09-29T07:33:44.871-04:002019-09-29T07:33:44.871-04:00Thank you for your guidance through this research,...Thank you for your guidance through this research, Debbie. I do appreciate it. Your notes of caution for peer reviewed journals and pedigree collapse are duly noted. The research wouldn't be fun if it were easy, right?Family Sleutherhttps://www.blogger.com/profile/11584864778317578299noreply@blogger.comtag:blogger.com,1999:blog-5826248344207578284.post-43309309350066839242019-08-26T07:13:18.343-04:002019-08-26T07:13:18.343-04:00A great blog post. I would add that since you are ...A great blog post. I would add that since you are tracing back to common ancestors in Virginia, where the population was very small at that time, you also need to consider the possibility that, because of pedigree collapse and the founder effect, you are related to your matches not just through the ancestral couple of interest but through other pathways as well. Sharing multiple ancestral pathways increases the chances of matching a cousin but also makes it more difficult to determine which pathway the match is on. Bottlenecks and pedigree collapse also have the effect of reducing genetic diversity so you end up with segments that are widely shared in a particular population.<br /><br />We also need to remember that publication in a peer reviewed journal is not a guarantee of quality. It merely helps to filter out some of the lower quality articles. Also genealogical journals will not generally have population geneticists on their editorial board so the reviewers might not be in the best position to review such articles. Debbie Kennetthttps://www.blogger.com/profile/11573470282571579765noreply@blogger.comtag:blogger.com,1999:blog-5826248344207578284.post-47570519259500569422019-08-19T08:41:36.536-04:002019-08-19T08:41:36.536-04:00I agree (especially since your ancestors appear no...I agree (especially since your ancestors appear not to have been endogamous so those amounts are more reliable). Amyhttps://www.blogger.com/profile/15720293202890878993noreply@blogger.comtag:blogger.com,1999:blog-5826248344207578284.post-34234269358192699642019-08-19T07:18:03.446-04:002019-08-19T07:18:03.446-04:00Thank you, Louis. Can you point me to any online g...Thank you, Louis. Can you point me to any online guidance on how best to follow this approach? Would my starting point still be these 4th great-grandchildren of the MRCA from whom I speculate Thomas and Mary descended or myself? Family Sleutherhttps://www.blogger.com/profile/11584864778317578299noreply@blogger.comtag:blogger.com,1999:blog-5826248344207578284.post-71477519577209272122019-08-19T07:08:16.323-04:002019-08-19T07:08:16.323-04:00The amounts of shared DNA vary depending on the re...The amounts of shared DNA vary depending on the relationship level, but all fit within the expected range for the particular relationship level (so 4th great-grandchildren of the speculated MRCA share more than the 5th and 6th great-grandchildren who I've located).<br /><br />For those 4th great-grandchildren matches the average shared cM is 20. Seems like a reliable amount to me.Family Sleutherhttps://www.blogger.com/profile/11584864778317578299noreply@blogger.comtag:blogger.com,1999:blog-5826248344207578284.post-80677195057742709292019-08-19T06:59:55.021-04:002019-08-19T06:59:55.021-04:00I'm not familiar with Brecher's tool, but ...I'm not familiar with Brecher's tool, but in reading about it I see how it clusters AncestryDNA's shared match list. <br /><br />I'd like to give this a go. Is this the link that you used: <br /><br />https://github.com/jonathanbrecher/sharedclustering/wiki ?Family Sleutherhttps://www.blogger.com/profile/11584864778317578299noreply@blogger.comtag:blogger.com,1999:blog-5826248344207578284.post-78030004374312396992019-08-18T17:07:32.151-04:002019-08-18T17:07:32.151-04:00You are correct. Working top down from a specific ...You are correct. Working top down from a specific ancestor 5 or more generations back will likely not result in enough triangulations to work with. <br /><br />Triangulations work better when you do them bottom up, by determining for a particular triangulation group, first the parent, then grandparent, working up the ancestral path as best you can. This is like DNA painting but using triangulations instead of single matches.Louis Kesslerhttps://www.blogger.com/profile/11704667321407909489noreply@blogger.comtag:blogger.com,1999:blog-5826248344207578284.post-80563710362729731982019-08-18T15:45:12.292-04:002019-08-18T15:45:12.292-04:00Great post, Michael. You've done a wonderful j...Great post, Michael. You've done a wonderful job of explaining all this. It is so hard to find anything too conclusive about those descended from a MCRA going that far back based on DNA because of all the reasons (and math) you described. But if the descendants of the two presumed siblings share a fairly telling amount of DNA, that would seem to bring you pretty close to your conclusion without triangulation, doesn't it? Or are the amounts shared too small to be reliable?Amyhttps://www.blogger.com/profile/15720293202890878993noreply@blogger.comtag:blogger.com,1999:blog-5826248344207578284.post-75388516301072438432019-08-18T12:24:59.244-04:002019-08-18T12:24:59.244-04:00Have you tried Jonathan Brecher's Shared Clust...Have you tried Jonathan Brecher's Shared Clustering, an Open Source tool for generating cluster diagrams from DNA match lists on Ancestry? This may be an alternate approach to finding similar matches, i.e. people who share a segment which comes from one ancestor as opposed to an ancestral couple. I'll send you the link to the GitHub wiki if you are interested. Cathy Meder-Dempseyhttps://www.blogger.com/profile/14430219440977503623noreply@blogger.com