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Archiver > GENEALOGY-DNA > 2002-04 > 1019503772


From:
Subject: Re: [DNA] Relative Genetics/Ancestry.com results
Date: Mon, 22 Apr 2002 15:29:32 EDT


In a message dated 04/22/02 10:37:30 AM Pacific Daylight Time,
writes:


> Ancestry has some nice verbiage associated with the test results of the
> type that visitors to their web site will recognize right away. There
> is one thing that is worth pointing out under the heading of "Most
> Recent Common Ancestor" that raised some questions in my mind based on
> statistics that I have seen earlier. It is:
>
> # of Mismatches - 0
> Median Number of Generations - 3.6
> Possible Range in 95% Interval - 0.1 to 19.2
>
> # of Mismatches - 1
> Median Number of Generations - 8.9
> Possible Range in 95% Interval - 1.3 to 29.7
>
> # of Mismatches - 2
> Median Number of Generations - 14.5
> Possible Range in 95% Interval - 3.4 to 39.3
>
> Compared to the numbers that we have seen reported here earlier, these
> are way too small. Assuming that this is incorrect, this is a serious
> error and problem for Ancestry users.

I checked these numbers against my Most Recent Common Ancestor (MRCA)
Calculator http://members.aol.com/dnacousins/MRCA.exe. In fact, I wonder if
they are using my calculator. Scott Woodward asked for my source code a while
back, saying he wanted to extend the calculator to a higher number of
mutations. But if Relative Genetics only goes to two mutations, perhaps they
had a harder time extending the calculator than they expected. I stopped at
two. because the equation even for two mutations is quite complex.

Anyway, it appears that Relative Genetics is using an average mutation rate
of .004 per locus, while Family Tree DNA is using .002. Bruce Walsh has some
discussion of mutation rates at

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

The .004 number has been reported by Holtkemper, based on a study of sperm.
If you search our archives for Holtkemper or sperm, you can probably find
some discussions on whether it's appropriate to use .004. However, Brett
intimated in a message a while ago that Relative Genetics is using mutation
rates derived from their in-house database. There's been very little reported
in the scientific literature on mutation rates for markers beyond the core
group that everyone uses.

Ann Turner
GENEALOGY-DNA List Administrator
http://lists.rootsweb.com/index/other/Miscellaneous/GENEALOGY-DNA.html




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