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From:
Subject: Re: [DNA] Measuring Genetic Distances [DYS464]
Date: Tue, 25 Nov 2003 14:43:10 -0700
References: <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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