**GENEALOGY-DNA-L Archives**

From:Subject:Re: [DNA] Measuring Genetic Distances [DYS464]Date:Tue, 25 Nov 2003 14:43:10 -0700References:<1d2.14e9aeb4.2cf502c0@aol.com>In-Reply-To:<1d2.14e9aeb4.2cf502c0@aol.com>Ann Turner writes:

". It seems contradictory to call it a rapidly changing marker, but then

apply the infinite allele model. Could you elaborate on that?"

The IAM (Ininite allales model) provides a very close approximation for the

distribution of times to MRCA when the number of differences is very small (say

1 or 2 markers out of 25). The stepwise model is more apporpriate if we are

assuming that (i) the stepwise single step mutation model holds for the data

and (ii) there are some two (or more) step differences and/or fair number of 1

step differences. You can compare the distribution of times for (say) 23-2-0,

23-1-1, and 23-0-2 (23 exact matches - x off by 1 - y off by two) at

http://nitro.biosci.arizona.edu/ftDNA/TMRCA.html

to see the difference between the IAM and stepwise models. The IAM model scores

all three of these as 23 matches and 2 mismatches, while the stepwise model

weights the actaul number of steps off when considering the time to MRCA.

Cheers

Bruce

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