Time to Most Recent Common Ancestry Calculator,

Using Genetic Marker Similarity Between Two Individuals

 You are visitor number   since 23 Jan 2002 

Current Version: 16 December 2003

A service of Family Tree DNA

Method: Walsh, Bruce , 2001. Estimating the time to the MRCA for the Y chromosome or mtDNA for a pair of individuals, Genetics 158: 897--912

Details:

TMRCA For Y chromosome data

Select the degree of matching between the two individuals:

What is the effect of adding even more markers?

Adding additional markers increases the precision of the test. For example (assuming the standard mutation rate),

While there is a fairly dramatic improvement in going from 12 to 21 markers, a comparable improvement (i.e., having the 50% probability be 4 generations) requires scoring 43 markers. With a 100 markers, the 50% probability corresponds to 2 generations (exact value 1.7).

Under the standard mutation rate (0.002 = 1/500), the number of generations giving 50% probability has a very simple form. If two individuals match at all n markers, then the 50% time is

Here's this function plotted for 10 to 50 markers

One can also the effect of adding additional markers by looking at the cumulative probability curves for the time to MRCA for a pair of individuals with a complete match at 12, 25, and 37 markers. The black horizontal lines correspond to 2.5, 50, and 97.5 percent (the 95 percent confidence interval is given by the 2.5 to 97.5 interval).