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MRCA: What is it and what does it mean?
Ian — Thu, 03/05/2009 - 16:15
If you have participated in DNA Genealogy you may have seen the acronym MRCA. What does it mean? Well it is short for Most Recent Common Ancestor. MRCA is the first person that two different people share. For instance, I share my MRCA Robert Towler with a fellow Towler researcher. MRCA does not only apply to DNA testing, but it is often used often in this setting.
When you have your DNA tested you have the option of getting several different levels, 12 markers, 25 markers, 37 markers and 67 markers. The more markers you have tested, the more power that the results will have. The power comes in the ability to determine the MRCA. The more markers you have tested the narrower range you get for the MRCA between 2 people. As an example if 2 people are a 12 for 12 marker match they are 95% likely to have a MRCA within 29 generations of those tested. Now if you upgrade to the 25 marker panel and you are a 25 for 25 match the 95% likelihood to have a MRCA is 13 generations. If you jump to the most detailed test, 67 markers, and you are a match for 67 of 67 markers, then 95% likelihood for the MRCA is within 6 generations. For a full breakdown take a look at the table below that lists the probability for MRCA's:
Probability for Most Recent Common Ancestor (MRCA)
| Number of matching markers | 50% probability that the MRCA was no longer than this number of generations | 90% probability that the MRCA was no longer than this number of generations | 95% probability that the MRCA was no longer than this number of generat ions |
|---|---|---|---|
| 10 of 10 | 16.5 | 56 | 72 |
| 11 of 12 | 17 | 39 | 47 |
| 12 of 12 | 7 | 23 | 29 |
| 23 of 25 | 11 | 23 | 27 |
| 24 of 25 | 7 | 16 | 20 |
| 25 of 25 | 3 | 10 | 13 |
| 35 of 37 | 6 | 12 | 14 |
| 36 of 37 | 4 | 8 | 10 |
| 37 of 37 | 2 to 3 | 5 | 7 |
| 65 of 67 | 6 | 12 | 14 |
| 66 of 67 | 4 | 8 | 9 |
| 67 of 67 | 2 | 4 | 6 |
These results are based on Y-Chromosome DNA testing. The table clearly shows that the more markers you have tested the narrower the MRCA window becomes. As an example of the utility of this, I have proven using paper records 9 generations. So If someone is a 66 for 67 match to me, I know it has to be within the time period that I have documented. You can see the power of DNA testing, as it offers a piece of evidence that cannot be destroyed (burned or lost) over time.
Table and Image are borrowed from Familytreedna.com (http://www.familytreedna.com/faq-markers.aspx)