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Archiver > GENEALOGY-DNA > 2007-05 > 1179933386
From:
Subject: Re: [DNA] X chromosome, autosomes, and geographic projects
Date: Wed, 23 May 2007 11:16:26 EDT
In a message dated 5/22/2007 11:57:22 AM Pacific Daylight Time,
writes:
> Please let me know what may be learned by X and autosomal testing in a
> geographic project?
My personal opinion -- I don't think the current state of the art is good
enough to recommend it for a geographic project. I wouldn't feel comfortable
asking people to spend their money.
> Is testing CODIS markers the same as autosomal testing? I assume FTDNA's
> advanced orders includes some extra markers beyond the CODIS markers. Is the
> X chromosome included when people talk of autosomal testing? Which
> markers/panels are recommended?
CODIS markers, which are STRs, are one type of autosomal testing. DNAPrint
(Ancestry by DNA) uses SNPs. By definition, autosomal refers to non-sex
chromosomes, so the X is not included in that category. None of the CODIS markers are
on the X chromosome (nor DNAPrint's SNPs, to my knowledge). However, it has
some interesting properties (e.g. forming a haplotype in males, while undergoing
recombination in females) so it's worth studying.
> I'm wondering if autosomal testing may reveal a marker value shared by a
> large percentage of participants and if that marker value has a likely
> geographic origin
.
If you're referring to the CODIS-type markers, most values can probably be
found in most populations, just in differing percentages. You can look up the
raw data for sample populations in OmniPop.
If two people share the same value, it doesn't necessarily mean they
inherited it from a common ancestor. CODIS markers mutate at a rate similar to the
Y-STR markers, so the two people could be "Identical by State" or IBS. Sharing a
SNP is a stronger indication of common ancestry (being "Identical by Descent"
or IBD). SNPs have a very low mutation rate, and we sometimes treat them as
Unique Event Polymorphisms, mutations that have occurred only once in all of
human history (undoubtedly an exaggeration, but still a useful starting point).
Ann Turner
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