Maybe I'm not understanding this, but why would you want to test your brothers if you already have both of your parents tested? I had my father tested with the last FTDNA sale so I now have results at FTDNA for both parents. I thought I'd be able to determine IBD segments now. If this isn't the case all I have left to me is a half-brother (from my father) that could be tested. I hesitate to go down that path because I have zero interest in the matches that might come from my brother's maternal side. Thanks Greg Matthews On Fri, Jun 22, 2012 at 9:20 PM, Tim Janzen <[email protected]> wrote: > Dear Chris and Jim, > As a general rule for segments between 5 and 10 cMs in length if > both a parent and a child both have an HIR on the same segment that they > share with a match match at 23andMe or Family Finder, then that particular > segment is IBD. If the parent matches someone else, but the child doesn't > match that person then you can't be certain whether or not the segment is > IBD or IBS without more information. The more children that are tested in > situations like this, the higher the chance you will be able to determine > if > a segment if IBD or not. If you test 2 children and one parent then you > should be able to identify 75% of all IBD segments. If you test 3 children > and one parent then you should be able to identify 87.5% of all IBD > segments. If you test 4 children and one parent then you should be able to > identify 93.75% of all IBD segments. This is one of the main reasons I > plan > to do autosomal tests on my two brothers in the near future even though I > have already tested my parents. > Sincerely, > Tim Janzen > > -----Original Message----- > From: [email protected] > [mailto:[email protected]] On Behalf Of Jim Bartlett > Sent: Thursday, June 21, 2012 5:46 AM > To: [email protected] > Subject: Re: [AUTOSOMAL-DNA] Chromosome Browser > > Chris > > IBD means it's from an ancestor; IBS means it could have been contributed > by > a variety of ancestors, and it's just in the DNA "soup". But the segments > don't come with tags indicating which they are, so you don't know if a > segment is IBD or IBS. Some folks deal only with segments over 10-12cM or > so > to pretty much guarantee they are IBD and come from a specific ancestor. > > Jim > > > > ______________________________ > For answers to Frequently Asked Questions about mailing lists, please see: > http://dgmweb.net/MailingListFAQs.html > > > ------------------------------- > 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 >

Dear Greg, You should review your family's list of matches to see what percentage of your parents' matches are also matching you. In theory, 50% of your parents' matches should also match you on exactly the same segment. However, you will probably find that if you do this that the percentage of your parents' matches who also match you on exactly the same segment is somewhat less than 50%. This would suggest that a portion of your parents' matches who don't also match you are false matches (IBS). You don't necessarily have to test your half-brother. However, if you did then you could be reasonably certain that any people who match both your half-brother and your father but don't match you are IBD. That can be helpful information to have, particularly if the matching segment is fairly short. You don't need to pursue your half-brother's maternal matches. You only need to concentrate on your dad's matches. I think that the best way to illustrate this problem is to post again some information I shared with this list on Jan. 9 and Jan. 10. See below. A portion of our lower level matches are IBS. It would be nice to know that a match is IBD before you go to a lot of work trying to research someone else's family tree trying to find a genealogical connection. I want to review and research the family trees of people I am reasonably certain share a genealogical connection with me and I want to avoid reviewing and researching the family trees of people who are false matches (IBS) to my family. Sincerely, Tim I decided to download the Ancestry Finder matches from 23andMe for my parents, my wife's parents, my wife, and me. I then sorted the data to remove the anonymous matches. I then compared my wife's and my matches to our parents' matches to see if any of my wife's or my matches in Ancestry Finder were not found in the Ancestry Finder matches for our parents. Below is an analysis of the results: cMs %IBD %IBS >10 100 (51/51) 0 9-10 87 (14/16) 13 8-9 91 (31/34) 9 7-8 79 (33/42) 21 6-7 67 (65/97) 33 5-6 43 (80/185) 57 I decided to download the latest Family Finder data for my wife's parents, my wife, my parents, and me yesterday. I then analyzed the data so see how many people appear in the FF match lists for my wife and me who don't appear in the FF match lists of our parents. I then used that data to create my own statistics regarding the percentage of matches at various segment lengths in cMs to see how my data compares to the statistics that John Walden generated. Here are my results: cMs %IBD %IBS >11 100 (52/52) 0 10-11 80 (12/15) 20 9-10 93 (25/27) 7 8-9 81 (34/42) 19 7-8 46 (11/24) 54 6-7 67 (4/6) 33 5-6 40 (6/15) 60 4-5 20 (10/51) 80 3.5-4 17 (11/66) 83 Below are John Walden's results from his analysis that I posted in another message several days ago: cM %IBD %IBS 10 99 1 9 80 20 8 50 50 7 30 70 6 20 80 5 5 95 -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Greg Matthews Sent: Friday, June 22, 2012 7:59 PM To: [email protected] Subject: Re: [AUTOSOMAL-DNA] Chromosome Browser Maybe I'm not understanding this, but why would you want to test your brothers if you already have both of your parents tested? I had my father tested with the last FTDNA sale so I now have results at FTDNA for both parents. I thought I'd be able to determine IBD segments now. If this isn't the case all I have left to me is a half-brother (from my father) that could be tested. I hesitate to go down that path because I have zero interest in the matches that might come from my brother's maternal side. Thanks Greg Matthews