Galbraith DNA Testing MRCA Calculator

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Download MRCAChart-b.4.exe Copyright © 4/6/2004 BG Galbraith

This program is based on equations presented by Bruce Walsh in Genetics 158:897-912.

DNA Tests on the Y Chromosome of two Males can, by comparison, determine the approximate time back to a Most Recent Common Ancestor of the two persons. This program uses equations 12 and 14b from Bruce Walsh's paper to calculate the probability that the MRCA of two persons is less than or equal to a given number of generations, (t).

The calculator will accept as input any number of tested markers (n), markers that match (k), and the estimated mean mutation rate per marker per generation (u). Values of (u) normally used range from a low of .002 to a high of .004. There is still some doubt what mutation rate to use, but recent studies indicate an average value of .0048 is a fair approximation. FTDNA now has a proprietary copyrighted calculator that is somewhat more accurate than this simple one.

Output is in the form of a scrollable list box which presents the probability that MRCA is less than or equal to (t), given (n), (k), and (u) for 1 to 100 generations. It should run on all versions of MS Windows from Windows 95 or later.

One must first enter (n), (k), and (u). Then clicking on the <Calculate> button will present data in the scrollable list box. After the data is calculated, Clicking on the tab,<Graph MRCA> presents a chart of the output data.

Clicking on the tab, <Graph P(n-k|t)> presents a chart showing the probability of marker mismatches of 0 to 5 for any two persons at any given time , t , in generations for the given mutation rate, (u).

ACCURACY: For the case where all markers match, equation 14b in Walsh's paper was used to calculate (t) to three decimal place accuracy. For the cases where all markers don't match, a numeric integration (trapezoid rule) of equation 12 was used to calculate (t) to two decimal places. Because of this, errors of up to 2% may be expected for t > about 40 and u > about .004. (Entering a mutation rate larger than about 0.1 may cause the calculator to fail to calculate, since it will be trying to evaluate an expressions larger than the double-precision number format is capable of dealing with.)

This program may be freely used and distributed for non-commercial purposes.

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