Sunday, September 11, 2016

STR's And YFull

The STR values finally came in for Roger Forgey (descendant of Andrew Forgey and Margaret Reynolds). The STR values provided through the BigY test, and YFull, are said to be less reliable than the original FTDNA markers tests. The Big Y was not designed to be a marker test. It's designed to identify SNP's. Since our terminal SNP at this time is so old, about 800 years old, it isn't very helpful.  I see more potential in the STRs. Although if we had a closer cousin tester to Roger at Y-Full we would get a closer terminal SNP. Sounds like a combination of STR's and SNP's gives you an idea of how far back your common male ancestor lived? Still trying to understand all this.

I had hoped I could compare Roger's 37 marker test with Craig's 67 marker test. I was able to compare more markers; 61 to be exact. This does help. All matched except 3 . Another mismatch was found on a marker in the 67 marker range. The other two were in the 37 marker range. This means they still remain close matches. They probably share a common male ancestor back in the 1600's, as we already know from our paper trail.

I will upgrade my Uncle's test to the Big Y when there is a sale. That should help.

Right now Roger Forgey has 4 close matches on the STRs. Three of the four are Fergusons. The one is not in the Ferguson group, and doesn't have any surname posted. This could be a Stewart? This result makes me think the STR's though more prone to error with this particular test, are accurate enough to establish which matches are closest in time. We believe Forgey is a variant of Ferguson, and these results would seem to point in that direction. Matching up 400 STR's even if a few may be off by a digit would be great.

I have no idea what the significance of having 30 markers difference is at 400 markers? Not sure how far back in time that would put the common ancestor?

It appears that they were only able to get 431 good reads on Roger's STR's, out of 500. An average comparison of about 400 STR's between his matches. With 55 not available for comparison.

Going back to our about 800 year old terminal SNP. Four out of  seven of Roger's SNP I-B3819 matches are Fergusons. Y-Full estimates that the time to the most recent ancestor for I-BY3819 could be from 1250 years to 425 years ago. Not sure how they come up with these calculations which seem to disagree with one another? The Fergusons in the Ferguson group are actually more closely related  to each other with a newer, downstream, terminal SNP of I-BY3821 which they estimate has a Time To Most Recent Ancestor (TMRCA) of 800 to 275 years ago. They could all share a common male ancestor as recently as 275 years ago.

For those new to Y DNA testing SNPs are listed on a Y tree which looks like this:


Those related closer in time have SNP's farther down on the list, or downstream.

The STR's look like this:

The rows represent those tested. The columns are the values on each marker. The value numbers need to be exactly the same to match on that marker.

Upgrading another Forgey test to the Big Y will be helpful. It is very expensive so I wouldn't do it unless there is a good sale. Comparing 400 STR's could prove to be very helpful.

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