Poor 12-marker matches but good 37 and 67?

[neil_soton]

Hello

Would be grateful for any help to understand my results. I have done 67-marker test in the hope of finding a clue to the identity of the father of my illegitimate ggg-grandfather, born in Leicester, UK in 1856. While I have a lot of 0 difference 12-marker matches, none of these matches is anywhere near close at the 25-marker or higher level. On the other hand I have some very good 67 and 37 marker matches for which I have a difference of 2 at the 12-marker level. All these matches are with Ray/Rea or Morgan surnames.

Best match is with a Ray where I have a difference of 2 (28 cf their 30) at 389-2 in the first 12, but only one difference (12 cf 11 at 444) in the remaining 55 markers. I seem to differ by 2 at 389-2 with all my better matches, and only by 1-3 in the other markers.

Only explanation I can think of is that I have diverged from these matches by 2 at 389-2 since the MRCA. How recently could this be? I had thought that the first 12 markers were the slower moving ones, so wouldn't I expect more differences in the other markers?

Any help / advice / pointers very welcome indeed!!!

THanks

Neil

[J Honeychuck]

There's a paper on individual marker mutation rates at http://download.cell.com/AJHG/mmcs/j...04192.mmc1.pdf

Regards,
Jim

[Frederator]

It may be worthwhile to note that there is in no absolute biological sense a "sequence of priority" among the 67 markers which you have had tested. No individual marker or panel of markers is somehow more important than any of the others.

True, the geneticists that worked with FTDNA and other companies selected specific markers to test on some objective basis--I think based on the typically observed mutation rates in some sample population. But that's just a generalization for the population at large. Individuals must almost certainly deviate from the general pattern, although typically not by much.

That is why you did the right thing by going straight to the 67-marker test. The significance of individually aberrant mutations will wash out if you test a large enough number of markers. The accuracy of relationship predictions increases exponentially with each additional 12- or 13- marker panel you test.

I would advise against reading too much into the fact that specific individual markers within the first two panels may not match. What's important is that you have identified individuals with whom you have very few mismatches over a relatively large number of markers tested.

If you know all the allele counts for each marker for both yourself and your matches, you can calculate a very specific TMRCA calculation via the McGee Y Utility at http://www.mymcgee.com/tools/yutility.html

While this is neat, and I do recommend that you do so at some point, it is only a guess because, as I say, mutations are random. You and your nearest matches will have to do a really rigorous paper trail match to specifically identify how long ago you share a MRCA.

For my money, though, and since it is only just a guess, I just perform a 'back-of-the-envelope' style calculation. Example: Typical mutation rate of 0.5% per generation on each marker at 67 markers means that a man should experience a mutation roughly once in every 3 generations.

And for purposes of this rough calc, let's say that the average # of years between the birth of each generation is 30 years. Almost certainly not true for each individual case, but a useful generalization that smooths out anamolies.

Keep in mind that, for the purposes of the comparison, the assumption is that the person against whom you are comparing is related from some currently unknown point in time. So he should have a similar number of mutations from your MRCA as you do.

So here's the rough estimate of TMRCA for differences at 67 markers.

# Markers Diff. / # Generations / # Years
1 / 2 / 60
2 / 3 / 90
3 / 5 / 150
4 / 6 / 180
5 / 8 / 240
6 / 9 / 270
7 / 11 / 330

DON'T get too hung up on these calcs. 'Cause again, they're just a generalization. An educated guess. In the real world mutations are random and conform to this schedule only when averaged together for a very large population. Only your paper trail can prove for sure how far back you relate to a specific individual.

Good luck.

Hello

Would be grateful for any help to understand my results. . . .

[neil_soton]

Thanks very much for this really helpful advice. I tried the utility you linked to, and with my best (Ray) match at 67 markers this suggests TMRCA of 210 years at 50%, 330 at 75% and 540 at 95%. This seems a plausible fit as from the existing paper trail there can't be a common ancestor after 1780 (my ancestors are in the UK/Ireland whereas the Ray trail goes back to the 1780s in the US). Suggests that researching the Ray connection further would be a sound use of time, as there are only a few Ray/Wray families in Leicester at the time of my ggg-grandfather's birth in 1856 so only very few Ray/Wray candidates to be his father.

Any further thoughts on how to proceed, particularly from anyone who has wrestled with this kind of illegitimacy problem, would be very welcome!

Thanks again

Neil