Tuesday, June 18, 2013

The timing of DNA testing

We've just received the latest important SNP for our St Clair of Herdmanston test subject. He's confirmed P310+, P312-.

This is important because it's definitive. Even though the time frame that this SNP mutation occurred is quite old (about 4,300 years), it's absolutely certain that he shares an ancestor with everyone else who has this SNP.

How long does it take?

Explaining the timeline and order of events in DNA testing for genealogy helps new folks understand what to expect. I'll use our new St. Clair of Herdmanston test subject as an example.

4/3/2013 - Kit reached FTDNA's lab. (see a tour of the lab here)
4/16/2013 - 12 marker STR results completed
4/24/2013 - 25 marker STR results completed
4/25/2013 - 37 marker STR results completed
5/3/2013 - 67 marker STR results completed

Once his 37 or 67 STR markers were completed, I could look at the results and make an educated guess as to which SNP test he should take.

4/28/2013 - Ordered the P310 SNP test
5/16/2013 - P310 results completed
5/18/2013 - Ordered the P312 SNP test
6/17/2013 - P312 results complete

STRs first. SNPs next.

STRs are the gateway into DNA for genealogy. They point the way and help to determine recent relatedness. But too many people are using them to make claims. The reason they're unreliable for such claims is that the markers (otherwise known as alleles) mutate. They can mutate up or down. They can mutate on the same marker multiple times. And some of them mutate quite quickly. On average, they're now believed to mutate about once every 300 - 500 years.

SNPs are single-nucleotide polymorphisms. DNA folks just call them "snips" for short. They are believed to only mutate once, and then never again. This makes them much more useful for understanding ancient relatedness. Experts like Tim Janzen calculate the time to most recent common ancestor (TMRCA) for many of the SNP groups, then project administrators like me look at their calculations and apply them to our studies. These SNP experts look to studies like ours to verify their theories and to point the way to more SNPs.

The Sinclair St Clair DNA study is now focused heavily on SNPs. We encourage our members to test out to at least 67-markers so that we can more accurately predict which of the $39 SNP tests they should take.

Even when your STR markers are saying you match someone in a recent time-frame, it's important to verify it with a SNP test. We've read about one test subject who matched someone on 61 of 67 markers, and naturally assumed they were related. They weren't, and SNPs proved it. In fact, they don't share a common ancestor for several thousand years.

Read the full DNA and historical report on the Herdmanston lineage of the St. Clair family here.





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