Sunday, June 5, 2011

Most Recent Common Ancestor (MRCA)

Come one, come all. Get your DNA done! A 12-marker..., 25-marker..., 37-marker..., or even a 67-marker marker match is magic and magnificent! [Even more markers are now available.] Put your money down, spin the wheel, and find your ancestors. Its easy! Its fun! Step right up!

So goes the buzz. The DNA dimension of genealogy has exploded upon the stage. The problem is, many of the DNA products do not explain what the results will show until you have done the testing. How much money do you want to spend? How many markers should you do? Who are my ancestors anyway? Will I find my long lost relatives?

The chart to the right tries to show approximately what the DNA tests results demonstrate. For a 12-marker test, an exact match shows that you would share a common ancestor some 29 generations past. [Using 35 years/generation would be roughly 1015 years] Wow, I share, with my matches, a common ancestor some 1,000 years ago. Now if you have an exact 25-marker test, you would share a common ancestor some 13 generations ago. Let's see, that would bring you to (13 x 35) 455 years ago. This cuts in half the number of years from our common ancestor. Humm...a 37-marker exact match would place our common ancestor 7 generations back. Wow, only (7 x 35) 245 years. Just about the close of the French and Indian War in America. Now an exact 67-marker test would place our common ancestor just 6 generations back. That is roughly 210 years. (6 x 35) Wow, that is around 1800. At least some census data exist for most of the states. So, not much difference between the 37-marker and 67-marker tests. [Except for the money.]

So there you have it. [Plus or minus 5%.] A 67-marker test (exact match) can bring you to 1800. Step right up.


  1. Please allow me to ask your opinion. We did an Y-DNA relationship test based on 16 STR-markers. I wrote about it in my blog here. There was an exact match with 14 markers. Do you agree to the oral statement of the lab lady?
    Thank you.

  2. Sorry Peter, not able to get through to your blog. States it does not exist? There are certainly lots of oral statements.

  3. Hello Peter...have discovered your wonderful blog...lots of work your question RE: post of Sat., Feb. 2, 2013? Jerry

    1. Yes Jerry, that's correct. Peter

    2. Peter, not sure how to evaluate STR vs SNP? My DNA based upon SNP (single nucleotide polymorphism) STR stands for single tandum replacement [one codon vs two codon substitution. There is also a multiple variable tandum replacement. What haplogroup? Jerry