Jim, that's interesting, I can't follow  your argument.  Whereas my presentation was clear to me.  Maybe you're talking about closer cousins; my writing was about single segments.  And single segment matches only match ~1/2 of our fifth cousins.  My analysis: I got 1/2 my mom's variable DNA (hereafter referred to as DNA).  I got 1/2 my dad's DNA.  Ditto my sis. The 1/2 from my mom in common with my sis is 1/2 *1/2 =1/4 my genome.  Ditto my dad. So I have 1/4 + 1/4 = 1/2 my DNA in common with my sis.  (All on average of course,  I actually have 48% in common with my sis.) Similarly the odds that we each got the same 1/2 from each parent is 1/2 *1/2 = 1/4 of the genome where we are 100% IDENTICAL.  So of the 1/2 the genome where I match my sis 1/4 / 1/2  = 1/2 of it tells me nothing new at all because we are identical there.  And 1/2 of the other spots we match, we'll match, therefore, corroborating our match, 1/2 we won't match, therefore,  saying nothing.  And 1/4 of our genomes, we won't match the same people because we don't even match each other. Summary: 1/4th genome, we are totally different, therefore, having totally different matches.   1/4th totally the same, therefore, no new info by our matching. 1/4 genome HIBD because we both match the same people, thus corroborating our match (the chances that our parent was HIBS and we each are also HIBS is too small to consider) 1/4 each of our genomes--either HIBD or HIBS because we match someone and our sibling doesn't because we each got the same DNA from our "wrong" parent who doesn't match the person we each match. Different expression of bottom line: At only 1/4th of our genome will we hit the jackpot because we are only HIBD with our sib and also HIBD with our matches.  AKA Corroborated. At 1/4th of our genome we'll totally understand why we don't match the same people because we don't match each other. At 1/4th of our genome, we'll match because we are 100% identical there rather than HIBD.  Therefore, no new info.  AKA Not Corroborated (not anti-Corroborated either, i.e either HIBD or HIBS with our putative match) and we have all the same matches. At the other 1/4, we might be corroborated and we might not but we have a lot of different matches from our sib. I don't know what's so difficult. Message: 3 Date: Sat, 16 Nov 2013 11:31:31 -0500 From: Jim Bartlett  Subject: Re: [AUTOSOMAL-DNA] > 1. Re: Finding shared atDNA ancestry without phasing (Jim Bartlett) To: "autosomal-dna@rootsweb.com"  Message-ID: <699613D6-572D-415E-BE77-42FD47033576@verizon.net> Content-Type: text/plain; charset=us-ascii I'm not sure how my partly true response relates to the rest of your email.  I will admit, however, that what I often say is partly true. I prefer to say it's mostly true;>j. DNA is random, so many outcomes are possible.  For your discussion about siblings - let's say the atDNA from a parent can be aggregated into 4 groups: a, b, c and d; so a+b+c+d=1. You got say a+b=.5; your sibling got b+c=.5; you both got b, neither got d. Do the algebra and a=c and b=d. So the amounts in each category can be determined. Note a and b are rarely equal, although over a large enough sample the average would be.  This aggregate analysis is not the same as a Triangulation analysis of segments among cousins. When you have segments among you and two Matches, on the same area of a chromosome, you have Triangulation (Y=A=B=Y), the segments are IBD - the chances that any of these segments are IBS are slim (almost 0). It's hard to make a concrete statement and waffle it just a little to allow for that random possibility.  Triangulation analysis is not usually done among siblings and very close relatives - for two reasons: 1. The relationships and Common Ancestors are known 2. A large "segment" between siblings and close relatives will involve multiple ancestors. You get a whole chromosome - a very large "segment" - from a parent, even a grandparent. Clearly there are multiple ancestors in that segment when it's broken up by matches with distant cousins. To a smaller extent this is true with large shared "segments" with aunts/uncles or close cousins. In fact this is the case with many matching segments - they come from multiple ancestors - but the smaller segments are below thresholds and we'll never see any cousin Matches on those more distant ancestors. The point is to be prepared to break large segments into smaller ones.  Jim - Sent from my iPhone - FaceTime! On Nov 16, 2013, at 8:59 AM, jlerch1@lighttube.net wrote: > Jim's statement about the chances being slim that 3 have an IBS is only  > partly true. My sister has recently gotten her data, and as expected  > at 1/2 of my matches at the 5th cousin level do I match her. But of  > that 1/2, 1/2 of that is at places where our parents each gave each of  > us the exact same DNA, so at that 1/4th of our genomes we are like  > identical twins. So we only count as 1 person at that 1/4th of our  > genomes. (It actually is a slight bit of corroboration since my data  > was V2 and hers is V3 chip.) You need to use the Family Traits app on  > 23 to see if you are Full IBD there instead of HIBD.  >