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X-DNA Advanced Advanced topics about X-Chromosome matching and anthropologic blocks based on SNPs and/or STRs.

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  #11  
Old 28th November 2016, 11:09 AM
MMaddi MMaddi is offline
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Originally Posted by georgian1950 View Post
Hi John, how about trying the exercise I talked about in this thread? I would like to see if you get the results I predict (i.e. most kits triangulate on a handful of segments, suggesting that you share a common ancestor with the owners of those kits within the last 300 years).

There is really no point in random sampling until we prove or disprove my hypothesis about the common ancestor for most of us. If this common ancestor existed, that information would pretty much change everything.

Thanks,

Jack
I have an even better test of your hypothesis of a common ancestor going back 300 years. Use the GEDmatch tool called "GEDmatch Archaic DNA matches" at https://www.gedmatch.com/archaic1.php. Use the same low level of shared segment cM that you've used to claim a segment goes back to a common ancestor who lived 300 years ago. I believe you've told us that your methodology relies on segments below 5 cM, as low as 1 cM.

At the 1 cM level, I get all 22 chromosomes lit up with shared segments with these ancient DNA samples:

F999916 - LBK, Stuttgart, 7,000 years old
F999918 - Luxemburg, 8,000 years old
F999937 - Hungary, 7,200 years old
plus others that are several thousand years old, that are not as lit up, but still with many shared segments

At the 2 cM level, that reduces the shared segments significantly, but I still get multiple shared segments on multiple chromosomes with the three samples I mentioned above.

At the 3 cM level, I still get 7 shared segments with F999916, 2 shared segments with F999918 and 8 shared segments with F999937.

At the 4 cM level, I still get 1 shared segment with F999916 but none with the other two I mentioned above.

It's only at the 5 cM level that I don't share any segments with ancient DNA remains in the GEDmatch database.

My very sincere question is how can you be so sure that the tiny segments your methodology uses gives you shared segments that go back to a common ancestor 300 years ago? According to what I found any segment below 4 cM could easily represent a common ancestor several thousand years ago. Even at 4 cM, there's certainly a chance that the common ancestor is still thousands of years ago.

This proves to me that using shared segments below 5 cM, which is not recommended or used by the three testing companies, is not a wise decision when looking for common ancestry within a genealogical time frame. While segments below 5 cM may represent a common ancestor within the last few hundred years, there's not much assurance that that's true. Perhaps if you can come up with paper trail documentation to support a common ancestor, I could accept using segments below 5 cM, but without that I could as easily say that the common ancestor lived thousands of years.

If you disagree with this, please tell me what's wrong in my thinking.
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  #12  
Old 28th November 2016, 11:24 AM
georgian1950 georgian1950 is online now
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Quote:
Originally Posted by MMaddi View Post
If you disagree with this, please tell me what's wrong in my thinking.
Well, my current exercise uses default parameters.

As for comparisons with ancients, it is more like a parlour game. The science is not well developed on that.

Jack
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  #13  
Old 28th November 2016, 11:40 AM
MMaddi MMaddi is offline
yDNA: R-CTS2509; mtDNA: T2e
 
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Quote:
Originally Posted by georgian1950 View Post
Well, my current exercise uses default parameters.

As for comparisons with ancients, it is more like a parlour game. The science is not well developed on that.

Jack
Hmmm... to me a 1 cm shared segement is a 1 cM shared segment.

I don't see a difference if you apply it to two living individuals or one living individual and ancient remains. The same goes for a 2 cM segment or a 3 or 4 cM segment. The tool is still checking the database for a run of exactly matching segments of a sufficient size, whether it's comparing against a database of living individuals or ancient remains.

You'll have to come up with a more convincing reason than what you've given.
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  #14  
Old 28th November 2016, 12:36 PM
John McCoy John McCoy is offline
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Assessing the genealogical significance of short segments by means of a robust statistical analysis seems like a very difficult problem to me. I was able to think of a statistical experiment that I believe could tell us something about male versus female X matches, if anyone has the time to gather the data. That's as far as I have got!
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  #15  
Old 28th November 2016, 01:11 PM
georgian1950 georgian1950 is online now
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Originally Posted by John McCoy View Post
Assessing the genealogical significance of short segments by means of a robust statistical analysis seems like a very difficult problem to me. I was able to think of a statistical experiment that I believe could tell us something about male versus female X matches, if anyone has the time to gather the data. That's as far as I have got!
Again, my exercise uses default parameters, 7.0 cM and 500 SNP's.

Jack
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