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Archiver > GENEALOGY-DNA > 2004-12 > 1104268154


From: (John Chandler)
Subject: Re: [DNA] MRCA = 800 AD
Date: Tue, 28 Dec 2004 16:09:14 -0500 (EST)
References: <122820041935.26936.41D1B5830002B916000069382200734840050B989A0E00@comcast.net>
In-Reply-To: <122820041935.26936.41D1B5830002B916000069382200734840050B989A0E00@comcast.net>(fauxdk@comcast.net)


David wrote:
> Can you, Doug or John or others here who are math whizes devise
> something more systematic so we could factor marker value rarity
> into a decision - making algorithm of some kind?

The rarity of a marker value is just a signal that something useful
is sitting there. The interpretation must depend more on the age of
that marker value and less on the degree of rarity itself. In other
words, if an allele is rare because it never existed at all until
500 years ago, then sharing that allele means a relatively high
probability of MRCA within the past 500 years. (Of course, it's
more complicated than that, but you get the picture.) On the other
hand, an allele that is rare but has been floating around for
10,000 years doesn't do much to tilt the odds of a recent MRCA.

John Chandler


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