GENEALOGY-DNA-L ArchivesArchiver > GENEALOGY-DNA > 2008-11 > 1226528484
From: (John Chandler)
Subject: Re: [DNA] Trying to get a better feel for MRCA calculations
Date: Wed, 12 Nov 2008 17:21:24 -0500
In-Reply-To: <email@example.com> (message fromJonathan Day on Wed, 12 Nov 2008 10:11:06 -0800 (PST))
> I've finally extended my family tree back to the 1600s and have
> found that there are living pure-male-line descendants of a common
> ancestor from 6 generations back. This would seem like a reasonable
> distance to see some mutations. Provided I can persuade any of them
> to actually do the testing (which is by no means certain), is it
> possible to use that information to "tune" MRCA calculations at all?
That depends entirely on what you mean by "tune".
> (eg: If I can find two people willing to be tested who connect to me
> through this individual, can I reliably infer what his markers would
> have been, and thus perform the calculation with him as starting
If you can test descendants of three different sons of this individual,
then you can indeed infer his haplotype, unless you are unlucky enough
to have a marker on which no two descendants agree. Even then, if you
have three different, but contiguous, values, you will have a good
probability of being right if you pick the middle value. In principle,
these inferences could break down through parallel mutations along two
lines -- but the probability of that is very low in only 6 generations.
> Or use one other person's data to recalibrate the curve?)
What curve? You will certainly not be able to revise the probability
distribution of TMRCA for a given pair of haplotypes on the basis of
testing a handful of people.
|Re: [DNA] Trying to get a better feel for MRCA calculations by (John Chandler)|