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 On Wed, Nov 16, 2011 at 5:36 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... >

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. I also think the fact that many are having trouble finding Common Ancestors is primarily due to not having complete ancestral trees by both parties - there is a Common Ancestor, we just can't identify him/her/them. I think many of these CAs are further back, and FTDNA in particular has been very conservative in their estimates of which generation it is. They think they need to do this to "manage expectations", but they are masking where the real pay dirt may be - IMO. Jim - Sent from my iPhone - FaceTime! On Nov 17, 2011, at 5:33 AM, Ann Turner <[email protected]> wrote: > 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 > > On Wed, Nov 16, 2011 at 5:36 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...

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. > > > >

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?

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? >