GEN-MEDIEVAL-L ArchivesArchiver > GEN-MEDIEVAL > 1996-02 > 0823878056
From: Tom Thatcher <>
Subject: Re: Genetics and Genealogy
Date: Fri, 9 Feb 1996 15:00:56 GMT
In <> (Stewart L Baldwin)
>I have been following with interest the various discussions in this
>newsgroup regarding genetics and genealogy, and have decided to put in
>my two cents worth.
>Assumption 1: It should be relatively simple and inexpensive to
>extract DNA from a large number of living individuals, and enter the
>complete sequnces of base-pairs into a database (including the
>mitocondrial genetic data).
False. It will cost millions of dollars and take ten years to do this for
one person (actually, the human genome project is going to produce a sort
>Assumption 1a: Assumption 1 is true for individuals who have been
>deceased for a long time.
Also false. You may be able to determine the entire mtDNA sequence from
a long deceased individual by sequencing all the pieces and putting the
information together, but will get nothing more than fragments of
>The most useful examples seem to center around the Y chromosome, which
>is inherited intact (except for possible mutations) from the father,
>and mitochondrial DNA, which is inherited intact (same exception) from
>the mother. (I am assuming that there is no "crossing over" between
>the X and Y chromosomes.
Possibly some crossing over but none involing the elements unique to the
>Example 2: The early Irish pedigrees have many cases in the early
>Middle Ages in which two men were brothers, or were claimed by the
>pedigrees to be brothers, and each brother has descendants (or claimed
>descendants) in the direct male line who are still living today.
>Testing a large number of these descendants to see whether they had
>the same (or nearly the same) Y chromosomes might help to determine
>how reliable some of these early pedigrees are, although it might be
>difficult in some cases to tell the difference between undetected
>adulteries and innacurate historical records.
Let me just point out that this sort of study (and corresponding studies
on mtDNA in maternal lineages) are ONLY possible with Y cromosome and
mitochondrial DNA. You simply can not ask these questions outside the
constraint of direct maternal or paternal lineage. You can only get
useful chromosomal DNA from living people. Just try going back 4
generations. 1/16th of my DNA came from my great-great grandfather
Austin. 1/16th of my third cousin Bob's DNA also came from Austin.
But because that DNA assorts randomly in each generation, the amount
of Austin's original DNA that we share in common is 1/16x1/16, or 1/256.
The amount of work needed to find this DNA and prove that it wasn't a
statistical fluke would cost millions and take years, just for one
pair of third cousins. (Of course if Bob and I are both direct male
descendants of Austin, we will have identical or nearly identical Y
Given the constraints of developing maternal and paternal lineages,
the difficulty of obtaining samples, and the simple impossiblity of
doing any analysis NOT based on maternal or paternal lineages, I doubt
that genetic analysis will ever become a part of genealogical research,
except in a very few, limited number of cases.
Tom Thatcher | You can give a PC to a Homo habilis,
University of Rochester Cancer Center | and he'll use it, but he'll use it
| to crack nuts.
|Re: Genetics and Genealogy by Tom Thatcher <>|