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  #11  
Old 13th February 2018, 02:05 PM
benowicz benowicz is offline
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The problem with STRs is the possibility that a back mutation could obscure from view an original mutation. If, say DYS458, went from 19 to 20 and back again to 19, you would have no way of knowing, since you have only one donor as a reference point, not time series data, like a sample from each ancestor in the direct line of descent.

One crude way of estimating the relative accuracy of each marker array--not absolute, but in comparison to each other--would be to sum the mutation rates for all markers in the array. I did that using the FTDNA numbers reported in the McGee Utility--no idea whether they're considered up to date estimates--and this is what I found:

37 markers is about 80% more accurate than 25 markers
67 markers is about 47% more accurate than 37 markers, or about 165% more accurate than 25 markers

I haven't tested for 111 markers, so I didn't bother to calculate that out. But I think all the new markers have very low rates, around 0.2%. So I guess that

111 markers is about 243% more accurate than 25 markers, 91% more accurate than 37 markers, 30% more accurate than 67 markers.

Assuming the other markers in the proposed 500 marker array are also about 0.2%, I'd guess

500 markers would be about 950% more accurate than 25 markers, 480% more accurate than 37 markers, 295% more accurate than 67 markers, and 200% more accurate than 111 markers.

With each new STR marker tested, you become less susceptible to distortion through a weird back mutation on any one of them.

It's probably also a good deal for people in poorly studied subclades like DF27. An extremely high resolution STR test may not necessarily be more accurate than an SNP match, but for a lot of people it could be a good proxy. Or, indeed, the only option. There are a vast number of people, like me, who live in under-studied subclades. SNP testing doesn't do much for us because they haven't even identified the relevant SNPs.
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  #12  
Old 13th February 2018, 02:08 PM
benowicz benowicz is offline
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Assuming that people are willing to pay for a high resolution test, that is. The problem is there are all these people running around with useless 12 and 25 marker STR profiles.
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