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Old 18th February 2017, 11:06 AM
NCroots NCroots is offline
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Join Date: Feb 2015
Location: North Carolina
Posts: 193
Originally Posted by benowicz View Post
Using the 30 year generation convention, they're probably all around 6 gen. out from the common ancestor. So roughly 16% percent chance. Not encouraging, but not out of the question.

I have a match at 37-markers with a distance of 3 (34/37). Using the TiP calculator, this gentleman & I are predicted to share a MRCA within 12 generations with a probability of 90.31% (within 24 generations at 99.82%).

Using the MRCA Calculator from the Clan Donald USA site, set for 37-markers distance of 3, I get an estimate of 9 generations at .072. That's without Cumulative Probability because I didn't know what that meant.

We suspect a NPE in our paternal lineage and nailing down the exact date of our MRCA would help in proving or disproving our theory. Which is more reliable, the TiP Calculator or the MRCA Calculator?
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Old 18th February 2017, 04:27 PM
benowicz benowicz is offline
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Join Date: Oct 2016
Posts: 24
Actually, that chart I copied and pasted fits the fact situation you present of 2 donors with GD of 3 at 37.

The Macdonald calculator uses very slightly slower mutation rates than the TIP calculator. I think the TIP calculator may be using more up-to-date information, but the differences aren't normally enough to get me bothered for such a rough estimate.

The percentages posted in my chart are cumulative. 36.9% at 9 generations. The 0.072 % figure that you quote seems as if it is the non-cumulative figure. Apples and oranges.

I only ever pay attention to the cumulative figure. You can look up and compare the difference between the technical definitions of cumulative and non-cumulative risk if you want, but a good, safe approach is to go with the cumulative percentage. I think most people only pay attention to the cumulative.

Either TIP or Macdonald are good choices. TIP's mutation rates may be more up-to-date, but Macdonald's are close enough, and probably considered more conservative. Which I guess is good.
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Old 27th February 2017, 02:32 PM
mouseinhouse mouseinhouse is offline
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Join Date: May 2016
Posts: 11
>I don't think I had realised how much variability there could be in the data!

Yes, that's the way it often is. The issue is that over a short range of generations there can easily be zero, one, two or three changes. Over a longer range of generations all this variability smooths out, and we get the simple picture that all the introductory texts imply is normal. Over the short range, variability is normal -- not helpful, but normal. :-)

I agree that BigY testing of everyone involved would probably help resolve this - at a significant cost -- although there are no guarantees. Essentially you would be testing thousands of markers, instead of just a few dozen, and can even find new markers that are specific for your lineage. There is a good chance you'll be able to find among all these markers a set that lets you build a tree showing which markers arose in which sub-lineage. However, that still won't necessarily tell you in exactly which generation a change appeared, and therefore won't necessarily tell you who is a sibling and who is a first cousin, for example.

So a less expensive way to begin is to do BigY testing of one person, and find out if there are possible family-specific SNPs (private SNPs) in that lineage that give good quality (unambiguous) results in testing -- many private SNPs turn out to be poor quality, poor prospects for testing. If that first BigY produces promising lineage-specific SNP candidates, you can do another person's Big Y to narrow down the set of diagnostic SNPs to the most promising ones, or go straight to single SNP testing (US$17 ea. at YSEQ for custom tests) of the other relatives if there are just a few good candidates for lineage-specific SNPs. That's likely to be less expensive than BigY on everyone.

If anyone else in your terminal haplogroup but outside your lineage has already done BigY, then it will improve your odds of finding good lineage-specific SNPs because you can exclude the ones in common with that person. Check your haplogroup on the YFull tree for that.
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