Calculating the time to your
most recent common ancestor
This page computes probabilities for the time to the most recent common ancestor (abbreviated TMRCA)
shared by two persons with a DNA match. It works as well for Taylors (or
any surname) as it does for the McDonalds for whom it was intended. The
blocked this type of content on your browser.
It was developed by Doug McDonald
and originally published at
http://dna-project.clan-donald-usa.org/tmrca.htm. A new version
— much revised and including NextGen tests — has now been published
at that location.
You will need to enter three variables into the input boxes:
- Number of markers tested in common,
- Number of those markers that match
- Estimated average mutation rate. (Select from the guide he provides or
use your own.)
Then check the "cumulative probability" box and click the "create graph" or
"create list" button. The output will be generated below the buttons.
To recalculate, change one or more input variables and click the button
This program calculates the probability that two people have a certain number
of generations between them, based on the standard infinite alleles formula of Walsh. It calculates both the probability of being at an exact number of
"transmission events" between a certain pair of people and
the cumulative probability that the actual number of transmission events is less than
a certain value. It can list both result types in a table, or graph either
type. In either case the horizontal axis stops at the point where the
cumulative probability reaches 97.5% or 10 generations, whichever is longer.
Note that the number of transmission events is essentially twice the number of generations
back to the MRCA (Most Recent Common Ancestor).
Suggested values for the average mutation rate per marker per generation are given below. These are estimates
from all available sources by the author as of October 2006 and except for the FTDNA 12 set are still not very well determined.
The SNP rates are particularly poorly known. More up to date estimates
can sometimes be found in the
Rootsweb genealogy-dna mailing list archives.
|FTDNA Y12 STR: || 0.0020
||SMGF STR set (no 464): ||0.0021
||mtDNA complete genome||3·10‑6
|FTDNA Y25 STR: || 0.0023
||All 118 available Y STR: ||0.0025
||autosomal, X, and Y &SNPs ||1·10‑8
|FTDNA Y37 STR: || 0.0033
||mtDNA HVR: || 2·10‑5
|FTDNA Y67 STR: || 0.0028
|| 2·10‑6 |
This program was created by J. D. McDonald and is public domain.
See the October 2014 revision, which produces very different results.