But each atDNA segment, including the large one, could only come from one of the ancestors, wouldn't it? I'd add the American Colonists, particularly in the 1600s, to your list, Ann. Jim Bartlett On 11/17/11, Ann Turner<[email protected]> wrote: Yes, you have increased the chances of inheriting some DNA in common. This occurs a lot for some population groups that intermarry a lot (Ashkenazi Jews, Mennonites, island populations like Puerto Rico, etc.) Ann On Wed, Nov 16, 2011 at 6:22 PM, <[1][email protected]> wrote: > How does Family Finder handle it when 2 people have two sets of ancestors > in common. Is it likely that the relationship might be predicted to be > closer than it really is because you are matching DNA from both lines? > Thank > you. > ------------------------------- To unsubscribe from the list, please send an email to A[2][email protected] with the word 'unsubscribe' without the quotes in the subject and the body of the message References 1. mailto:[email protected] 2. mailto:[email protected]

Mary Alice, I agree with you! I can assure you that the Common Ancestors (husband/wife) that each of my atDNA matches and I agree upon, are not just surname matches, they are real people with birth, marriage, and death dates and places and, in all cases, at least two children: one child is my ancestor and the other child is the ancestor of my match. They are the same family for both of us in the same place and time. Each and every person in each of our direct lineages is a real person (incidently with a unique ahnentafel number). Almost all of these lines can also be found in trees at GEDmatch.com; FamilySearch.org; and usually other on-line sites as well as genealogy libraries. Are these 100 percent guaranteed, bet-the-farm certainties? Who can say that about any genealogy. And besides that, there could easily be an NPE in one or both of our lineages. If so - then clearly the atDNA segment we share could not have come through this line. There is always that possibility. These situations can only be uncovered by detailed Y-DNA and mtDNA testing to veryfy each and every paper link. There is also the possibliity that our shared atDNA segment came from a different Common Ancestor. In fact several of my atDNA matches and I have more that one set of known Common Ancestors - so a DNA segment could come from either one of the lines (but not both). I have now documented at least 7 sets of cousins (from first to 8th) among my ancestors. So a match with one of them in the path to theCommon Ancestor provides two possible paths for the DNA segment to come down to me. The difficulty in finding a Common Ancestor is mostly due, IMO, to not knowing all of our ancestors! At the 4th cousin level, I don't know 12.5 percent of my ancestors; at the 5th cousin level 25 percent; 6th cousin level 43 percent; 7th cousin level 58 percent, 8th cousin level 69 percent, etc. That represents a LOT of places a Common Ancestor could be hiding - maybe just beyond a brick wall, maybe well beyond that. It's no wonder we don't match many of our atDNA matches. But that won't stop me from trying ... Jim Bartlett On 11/17/11, M. A. Farrell<[email protected]> wrote: Jim, have a question for you: You wrote....."I have a long list of FF and RF atDNA matches; I email them and try to find a Common Ancestor. 37 of them and I have found a Common Ancestor, 5 of them at the 10th cousin level...." What proofs of these 'found' relationships do you require? Apparently, I am too much of a stickler for requiring to know, for sure, which persons/dates/places of the surname found, are in fact the source of some matching dna. Many matches can tell me they found a surname matching one of mine, but cannot identify the couple to the same extent that I can! Then, I am asked to confirm a relationship which may not exist. I choose not to, and am accused of not playing fairly! A random matching surname with no further matching of dates/places of birth, marriage, death, are not confirmed relationships in my mind. How about you? Mary Alice ________________________________________ PeoplePC Online A better way to Internet [1]http://www.peoplepc.com ------------------------------- To unsubscribe from the list, please send an email to A[2][email protected] with the word 'unsubscribe' without the quotes in the subject and the body of the message References 1. http://www.peoplepc.com/ 2. mailto:[email protected]

Yes and the Finnish. CeCe www.yourgeneticgenealogist.com www.studiointv.com ---------------------------------------- > Date: Thu, 17 Nov 2011 15:37:53 -0600 > From: [email protected] > To: [email protected] > Subject: Re: [AUTOSOMAL-DNA] Two sets of Common Ancestors > > > But each atDNA segment, including the large one, could only come from one > of the ancestors, wouldn't it? > > I'd add the American Colonists, particularly in the 1600s, to your list, > Ann. > Jim Bartlett > > On 11/17/11, Ann Turner<[email protected]> wrote: > > Yes, you have increased the chances of inheriting some DNA in common. This > occurs a lot for some population groups that intermarry a lot (Ashkenazi > Jews, Mennonites, island populations like Puerto Rico, etc.) > Ann

I love your attitude Jim! CeCe www.yourgeneticgenealogist.com www.studiointv.com ---------------------------------------- > Date: Thu, 17 Nov 2011 15:31:20 -0600 > From: [email protected] > To: [email protected]; [email protected] > Subject: [AUTOSOMAL-DNA] Finding Real Ancestors [was Numbers differences between FTDNA and 23 & me] > > > Mary Alice, > > I agree with you! > > I can assure you that the Common Ancestors (husband/wife) that each of my > atDNA matches and I agree upon, are not just surname matches, they are real > people with birth, marriage, and death dates and places and, in all cases, > at least two children: one child is my ancestor and the other child is the > ancestor of my match. They are the same family for both of us in the same > place and time. Each and every person in each of our direct lineages is a > real person (incidently with a unique ahnentafel number). Almost all of > these lines can also be found in trees at GEDmatch.com; FamilySearch.org; > and usually other on-line sites as well as genealogy libraries. > > Are these 100 percent guaranteed, bet-the-farm certainties? Who can say that > about any genealogy. And besides that, there could easily be an NPE in one > or both of our lineages. If so - then clearly the atDNA segment we share > could not have come through this line. There is always that possibility. > These situations can only be uncovered by detailed Y-DNA and mtDNA testing > to veryfy each and every paper link. > > There is also the possibliity that our shared atDNA segment came from a > different Common Ancestor. In fact several of my atDNA matches and I have > more that one set of known Common Ancestors - so a DNA segment could come > from either one of the lines (but not both). I have now documented at least > 7 sets of cousins (from first to 8th) among my ancestors. So a match with > one of them in the path to theCommon Ancestor provides two possible paths > for the DNA segment to come down to me. > > The difficulty in finding a Common Ancestor is mostly due, IMO, to not > knowing all of our ancestors! At the 4th cousin level, I don't know 12.5 > percent of my ancestors; at the 5th cousin level 25 percent; 6th cousin > level 43 percent; 7th cousin level 58 percent, 8th cousin level 69 percent, > etc. That represents a LOT of places a Common Ancestor could be hiding - > maybe just beyond a brick wall, maybe well beyond that. It's no wonder we > don't match many of our atDNA matches. But that won't stop me from trying > ... > > Jim Bartlett > > On 11/17/11, M. A. Farrell<[email protected]> wrote: > > Jim, have a question for you: > You wrote....."I have a long list of FF and RF atDNA matches; I > email them and try to find a Common Ancestor. 37 of them and I have found a > Common Ancestor, 5 of them at the 10th cousin level...." > What proofs of these 'found' relationships do you require? Apparently, I am > too much of a stickler for requiring to know, for sure, which > persons/dates/places of the surname found, are in fact the source of some > matching dna. > Many matches can tell me they found a surname matching one of mine, but > cannot identify the couple to the same extent that I can! Then, I am asked > to confirm a relationship which may not exist. I choose not to, and am > accused of not playing fairly! > A random matching surname with no further matching of dates/places of birth, > marriage, death, are not confirmed relationships in my mind. How about you? > Mary Alice > ________________________________________ > PeoplePC Online > A better way to Internet > [1]http://www.peoplepc.com > ------------------------------- > To unsubscribe from the list, please send an email to > A[2][email protected] with the word 'unsubscribe' without > the quotes in the subject and the body of the message > > References > > 1. http://www.peoplepc.com/ > 2. mailto:[email protected] > > ------------------------------- > 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

Paul, I am under no delusions. I have a long list of FF and RF atDNA matches; I email them and try to find a Common Ancestor. 37 of them and I have found a Common Ancestor, 5 of them at the 10th cousin level. As a genealogist, I am dlighted - we share lineages and records and other infomation. I also record the fact that we share a [usually one] large [over 7cM] segement of atDNA. I note the Chromosome and length and starting point. I put this in an excel spreadsheet along with my ahnentafel numbers leading up to the Common Ancestors [we can't really tell which one of the husband/wife team the atDNA came from]. I sort this by Chromosome and starting point, and manually look for patterns in the ahnentafel numbers. One a very few patterns so far. But as my database grows, I'll find more .... I don't yet know if the atDNA segment has followed the same path as the paper trail. I've researched a fairly robust family tree since 1974, but there are a lot of unknown ancestors in it. In the mean time, I know for sure, I have a paper trail to a Common Ancestor. That too, will need to stand the test of peer review, and someday, even more robust DNA tools. I'm looking forward to it. Jim Bartlett On 11/17/11, Paul Wright<[email protected]> wrote: It should also be noted that many of the smaller segments (under 7 cM) that are included and viewable at FTDNA and included in their total share algorithm may very well originate with a different ancestor than the one responsible for the larger (over 7 cM) segment share. As such, for individuals with less diverse ancestry, this along with the randomness of recombination, results in a tendency to predict many relationships as being more recent than they really are. Meanwhile a number of people who find any paper trial connection with a genetic cousin and automatically assume the shared DNA originates with that paper trial connection, may be mistaken and should be cautioned with regard to more distant relatives, unless they have a wider array of known and more recently related relatives to also compare and help walk them (and their genetic cousin) back to the common ancestor responsible for the largest segment share. The potential impact of unknown NPEs or what some theorize as shared DNA coming from very ancient common origins (i.e. middle ages and predate genealogical records) may imply additional uncertainty. On Thu, Nov 17, 2011 at 7:39 AM, Jim Bartlett <[1][email protected]>wrote: > > You can see down to 1cM segments at FTDNA, but when you contact a match, > looking to find a Common Ancestor, all of the FTDNA, and 23&Me, matches > have at least one segment that is 7cM long or more. Restricting myself to > FF and RF, I can't contact someone with only a 5cM long segment. > > > > ------------------------------- To unsubscribe from the list, please send an email to A[2][email protected] with the word 'unsubscribe' without the quotes in the subject and the body of the message References 1. mailto:[email protected] 2. mailto:[email protected]

Jim, have a question for you: You wrote....."I have a long list of FF and RF atDNA matches; I email them and try to find a Common Ancestor. 37 of them and I have found a Common Ancestor, 5 of them at the 10th cousin level...." What proofs of these 'found' relationships do you require? Apparently, I am too much of a stickler for requiring to know, for sure, which persons/dates/places of the surname found, are in fact the source of some matching dna. Many matches can tell me they found a surname matching one of mine, but cannot identify the couple to the same extent that I can! Then, I am asked to confirm a relationship which may not exist. I choose not to, and am accused of not playing fairly! A random matching surname with no further matching of dates/places of birth, marriage, death, are not confirmed relationships in my mind. How about you? Mary Alice ________________________________________ PeoplePC Online A better way to Internet http://www.peoplepc.com

Yes, and you about 25% of your matches should overlap - close to your DNA share % with him, but subject to make up of the database and mix of your other ancestors and recombination. Just keep in mind that "roughly" 1/3 of the matchs that you and your sister have that do NOT match with your uncle will also be from your dad's side and "roughly" 2/3s will be from your mom's side. On Wed, Nov 16, 2011 at 8:28 PM, <[email protected]> wrote: > My sister and I and my dad's brother have all tested. Those matches that > my dad's brother shares with me and those he shares with my sister are for > sure related on my dad's side, right? This seems obvious, but so many > things that seem obvious in this game turn out not to be so, so I thought > I'd > ask. :) > > ------------------------------- > 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 >

There are gender specific differences in their X share algorithm (i.e. male vs male, male vs female, female vs female) On Thu, Nov 17, 2011 at 11:09 AM, Max Heffler <[email protected]> wrote: > 23andMe will also show X choromosome matches less than 5 cM. I think 3 cM > might be the cutoff. > > --

Ann, I think I have a set that I can send you. I could also send you mine and my parents, but my dad is at FTDNA and my mom is at 23andMe, so I don't know if that would work. CeCe www.yourgeneticgenealogist.com www.studiointv.com ---------------------------------------- > From: [email protected] > Date: Thu, 17 Nov 2011 08:19:52 -0800 > To: [email protected] > Subject: Re: [AUTOSOMAL-DNA] Fundamental autosomal DNA question > > No, unfortunately. I need raw data with father/mother/child trios on both > sides of the match so I can use phased data. That's not easy to come by. > > Ann > > On Thu, Nov 17, 2011 at 7:41 AM, CeCe Moore <[email protected]> wrote: > > > Ann, > > Thanks for sharing your experience. > > Have you looked at the raw data on those long segments (over 10 cM) to > > determine if they really are IBS? I find those lengths very surprising. > > With your data, you noted that about 95 percent of the time what I said > > earlier will hold true, but that other 5 percent is troubling. I certainly > > would like us all to be able to be confident of the validity of the 10 cM > > blocks and above, if not the 7 cM and above. > > CeCe > > Sent via BlackBerry by AT&T > > > > -----Original Message----- > > From: Ann Turner <[email protected]> > > Date: Thu, 17 Nov 2011 12:19:52 > > To: <[email protected]> > > Subject: Re: [AUTOSOMAL-DNA] Fundamental autosomal DNA question > > > > One way to study the problem is with father/mother/child trio data. If the > > child has a match not found in either parent, it is possible (indeed I'd > > say likely) that the segment is Identical by State, not Identical by > > Descent. > > > > Ancestry Finder at 23andMe lets you look at segments down to 5 cM / 700 > > SNPs. For actual numbers in one case, my son has a total of 231 segments > > listed with names attached. 67 of those are found only in the child (29%). > > The breakdown by segment size is > > > > 4/76 > 7 cM, longest 11.1 cM (5%) [This seems consistent with a 95% > > confidence interval] > > 7/37 6-7 cM (19%) > > 56/119 < 6 cM (47%) > > > > FTDNA seems to have a cutoff of 7.7 cM / 500 SNPs (that's by empirical > > observation -- has anyone found a shorter longest segment?). I have data > > for one father/mother/child trio that seems particularly dicey, with 22/100 > > matches in the child not found in either parent. The segment sizes ranged > > from 7.7 to 12.90, with a median of 8. Other trios I've looked at seem to > > run about 15%. > > > > Ann Turner > > > > On Wed, Nov 16, 2011 at 1:02 PM, CeCe Moore <[email protected]> wrote: > > > > > > > > When I say "legitimately" match, I mean an IBD segment that would meet > > the > > > company's matching threshold, not a segment made up of stretches of IBD > > and > > > IBS pieced together. > > > > > > I'm not saying that it is impossible for a match over ~7 cMs to be IBS, > > > but very unlikely. (I was going to write ~10 cMs in my response, but > > > thought that might be a bit conservative.) I know that it is > > theoretically > > > possible, but in my thousands of hours of atDNA research, I have yet to > > see > > > proof of one. Can you please show me an example of an IBS match over 7 > > cMs? > > > (I know that Ann Turner has seen lots of them between 5cMs-7cMs. We'll > > see > > > if she responds with a larger one.) > > > > > > If enough of a portion of the segment is IBS that it doesn't show up in > > > your parent (i.e.- make the company's threshold), then it will obviously > > > reduce the authentic match to a point that is not worth pursuing. I have > > > chased far too many matches under 7 cMs to recommend doing the same. > > > > > > > ------------------------------- > > 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 > > > > ------------------------------- > 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

It should also be noted that many of the smaller segments (under 7 cM) that are included and viewable at FTDNA and included in their total share algorithm may very well originate with a different ancestor than the one responsible for the larger (over 7 cM) segment share. As such, for individuals with less diverse ancestry, this along with the randomness of recombination, results in a tendency to predict many relationships as being more recent than they really are. Meanwhile a number of people who find any paper trial connection with a genetic cousin and automatically assume the shared DNA originates with that paper trial connection, may be mistaken and should be cautioned with regard to more distant relatives, unless they have a wider array of known and more recently related relatives to also compare and help walk them (and their genetic cousin) back to the common ancestor responsible for the largest segment share. The potential impact of unknown NPEs or what some theorize as shared DNA coming from very ancient common origins (i.e. middle ages and predate genealogical records) may imply additional uncertainty. On Thu, Nov 17, 2011 at 7:39 AM, Jim Bartlett <[email protected]>wrote: > > You can see down to 1cM segments at FTDNA, but when you contact a match, > looking to find a Common Ancestor, all of the FTDNA, and 23&Me, matches > have at least one segment that is 7cM long or more. Restricting myself to > FF and RF, I can't contact someone with only a 5cM long segment. > > > >

23andMe will also show X choromosome matches less than 5 cM. I think 3 cM might be the cutoff. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Ann Turner Sent: Thursday, November 17, 2011 10:52 AM To: [email protected] Subject: Re: [AUTOSOMAL-DNA] Numbers differences between FTDNA and 23 & me Yes, the matches you see at FTDNA and23andMe must have at least one long segment, and the great majority (but not 100%) should be IBD. The issue comes up more with people using 3rd party tools, like GEDmatch, where you can set the threshold lower. The important thing is just to keep an open mind about your conclusions. This applies to the segments where you have found a paper connection, too. The match is not *necessarily* through the line you identified, particularly when you get to the 4th cousin level or so. As a side note, 23andMe will display 5 cM relatives in Relative Finder if you are sharing genomes. The theory is that you invited someone to share because you have some "prior knowledge" that would tilt the odds in your favor. I suspect that worked out well in the case of my husband, who received his first close match in the Turner Y-DNA project after many years. The other fellow had also tested at 23andMe, and by sharing genomes, we could see a 6 cM segment in common. I'm inclined to think that falls in the pool of true positives. Ann

Quoting Greg Matthews <[email protected]>: > FTDNA's chromosome browser will give you the total segments shared. THank you. I'll try this asap. > > On Wed, Nov 16, 2011 at 8:36 PM, <[email protected]> wrote: > >> Could someone kindly enlighten me on the difference between the >> numbers used by both sources to identify matches? I get the basic 5 cM >> and 7+cM difference. But (1) what does 23 & me's "0.18%, 1 segment" >> mean? And is it important that FTDNA while giving you a total for >> "shared DNA" doesn't actually tell you over how many segments? Should >> you assume something anyway? It would be nice to know the answers >> before dealing with the large lists of matches...

Quoting Ann Turner <[email protected]>: > The Relative Finder percent is based on a total of ~7500 cM (two copies of > the genome), so 0.18% would be 13.5 cM. This number is comparable to what > you hear quoted for % DNA shared by various degrees of relationship, e.g. > > sibling 50% > 1st cousin 12.5% > 1st cousin once removed 6.25% > 2nd cousin 3.125% > 3rd cousin 0.78% > > You can see the size of individual segments if you share genomes and use > the Family Inheritance: Advanced tool (down to 5 cM). At FTDNA, you can see > this in the Chromosome Browser, down to 1 cM fragments. The great majority > of segments under 5 cM are likely to be pseudo-segments, though. FTDNA will > predict 3rd cousin relationships based just on the size of the longest > fragment, but 3rd cousins typically have more than one segment over 5 cM in > size. > > Ann Turner Thank you so much for these explanations. I'm going to save your message, because I need to get a more powerful computer to access and use the tools you mention (I'm using a friend's old clonker!). One more baby question (I hope you don't mind). When you say that 0.18%= 13 cM does this refer to the "total shared" or to the "longest block"? I would assume the former but am not sure. Also: where FTDNA says that a match has a "longest block" of 12 cM and a total shared of "46 cM" I can assume (they say it's a "4t5h or distant") that a few other blocks of these 46 are also more than 5 cM?

Dear Tim, To hopefully clarify my question, I meant from my paternal grandmother's X which to me meant my father's family. Could you please explain your answer? Do you mean my brother is only receiving his X from our mother and nothing from our father's mother? My brother and I only share 1/2 base pair on our X. My paternal uncle and I share several long blocks on our X,some are 1/2 and others have green stripes [full]. Is this just coming from my paternal grandmother and not my paternal grandfather's mother? Which grandmothers contribute to our combined ch. X? From your answer I'm assuming that my brother can only receive his from our mother because he is XY but I can receive it from both of my grandmothers since I'm XX. Could you please explain to me how this works? We were tested by Family Tree dna and our ch.X results were not given to us. Thanks. Fran

Dear Fran, Your brother got his Y chromosome from his father and his X chromosome from his mother. It always happens that way unless there is some unusual genetic abnormality such as Klinefelter's syndrome (XXY), or some other situation in which a male gets more than 2 sex chromosomes. Females get one X chromosome from their father and one X chromosome from their mother, unless there is some unusual genetic abnormality such as Turner's syndrome (X). Your brother thus only matches you on one of your X chromosomes. The matching blocks on the X that you share with your paternal uncle are likely coming from your paternal grandmother since your uncle received his X chromosome from your paternal grandmother. Your brother should not be sharing any large segments on the X with his paternal uncle. To better understand how the X chromosome is inherited I would suggest that you review the charts at http://www.thegeneticgenealogist.com/2008/12/21/unlocking-the-genealogical-s ecrets-of-the-x-chromosome/. Sincerely, Tim Janzen -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Frances Meng Sent: Thursday, November 17, 2011 7:19 AM To: [email protected] Subject: [AUTOSOMAL-DNA] Base Pair With Full Match Dear Tim, To hopefully clarify my question, I meant from my paternal grandmother's X which to me meant my father's family. Could you please explain your answer? Do you mean my brother is only receiving his X from our mother and nothing from our father's mother? My brother and I only share 1/2 base pair on our X. My paternal uncle and I share several long blocks on our X,some are 1/2 and others have green stripes [full]. Is this just coming from my paternal grandmother and not my paternal grandfather's mother? Which grandmothers contribute to our combined ch. X? From your answer I'm assuming that my brother can only receive his from our mother because he is XY but I can receive it from both of my grandmothers since I'm XX. Could you please explain to me how this works? We were tested by Family Tree dna and our ch.X results were not given to us. Thanks. Fran

You got it. On Wed, Nov 16, 2011 at 6:28 PM, <[email protected]> wrote: > My sister and I and my dad's brother have all tested. Those matches that > my dad's brother shares with me and those he shares with my sister are for > sure related on my dad's side, right? This seems obvious, but so many > things that seem obvious in this game turn out not to be so, so I thought > I'd > ask. :) > > ------------------------------- > 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 >

Yes, you have increased the chances of inheriting some DNA in common. This occurs a lot for some population groups that intermarry a lot (Ashkenazi Jews, Mennonites, island populations like Puerto Rico, etc.) Ann On Wed, Nov 16, 2011 at 6:22 PM, <[email protected]> wrote: > How does Family Finder handle it when 2 people have two sets of ancestors > in common. Is it likely that the relationship might be predicted to be > closer than it really is because you are matching DNA from both lines? > Thank > you. >

Yes, my son had a segment match today at 3 cM and just 281 SNPs.  He and his mother matched the person on chromosome 3 (8 cM with 1175 SNPs for my wife and 9 cM and 1278 SNPs for my son), but my wife didn't meet the threshold for the chromosome X match. Regards, Larry ________________________________ From: Max Heffler <[email protected]> To: [email protected] Sent: Thursday, November 17, 2011 12:09 PM Subject: Re: [AUTOSOMAL-DNA] Numbers differences between FTDNA and 23 & me 23andMe will also show X choromosome matches less than 5 cM. I think 3 cM might be the cutoff.

If you can use a web browser to see your results at FTDNA or 23andMe, the tools I mentioned should work OK. When the percentages at 23andMe say something like "0.39%, 3 segments", 0.39% would be the total. You also know that each segment is at least 5 cM. To get the exact lengths, you need to share genomes and look at Family Inheritance: Advanced. At FTDNA, it's usually NOT the case that other segments are longer than 5 cM when the relationship is unknown. In fact, I think FTDNA's 3rd cousin predictions are too optimistic when there's just one long segment. Ann Turner On Thu, Nov 17, 2011 at 8:18 AM, <[email protected]> wrote: > Thank you so much for these explanations. I'm going to save your > message, because I need to get a more powerful computer to access and > use the tools you mention (I'm using a friend's old clonker!). One > more baby question (I hope you don't mind). When you say that 0.18%= > 13 cM does this refer to the "total shared" or to the "longest > block"? I would assume the former but am not sure. Also: where FTDNA > says that a match has a "longest block" of 12 cM and a total shared of > "46 cM" I can assume (they say it's a "4t5h or distant") that a few > other blocks of these 46 are also more than 5 cM? >

Yes, the matches you see at FTDNA and23andMe must have at least one long segment, and the great majority (but not 100%) should be IBD. The issue comes up more with people using 3rd party tools, like GEDmatch, where you can set the threshold lower. The important thing is just to keep an open mind about your conclusions. This applies to the segments where you have found a paper connection, too. The match is not *necessarily* through the line you identified, particularly when you get to the 4th cousin level or so. As a side note, 23andMe will display 5 cM relatives in Relative Finder if you are sharing genomes. The theory is that you invited someone to share because you have some "prior knowledge" that would tilt the odds in your favor. I suspect that worked out well in the case of my husband, who received his first close match in the Turner Y-DNA project after many years. The other fellow had also tested at 23andMe, and by sharing genomes, we could see a 6 cM segment in common. I'm inclined to think that falls in the pool of true positives. Ann On Thu, Nov 17, 2011 at 5:39 AM, Jim Bartlett <[email protected]>wrote: > Thanks for this, Ann, > > You can see down to 1cM segments at FTDNA, but when you contact a match, > looking to find a Common Ancestor, all of the FTDNA, and 23&Me, matches > have at least one segment that is 7cM long or more. Restricting myself to > FF and RF, I can't contact someone with only a 5cM long segment. > > I thought the 7cM and 7.7cM segments were selected because of the very > high probability that they were IBD, and that the matches would indeed be > cousins, having a Common Ancestor from whom we both got that segment. > Please let me know if I've missed the fundamental concept here. >