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Archiver > GenChat > 1998-11 > 0912128294


From: Gethmann <>
Subject: [GenChat-L] Re: DNA testing
Date: Thu, 26 Nov 1998 20:58:14 -0400


(Joseph [Phil ] P Stevens) wrote:

> hi guys , Just curious , I am wondering if anyone has thought about
> doing a DNA test to prove there connection with a suspected anscestor ,
> And or asked about the costs involved , Phil...
>

Hi Phil,

Basically, this type of DNA testing to ancestors would be virtually impossible, except
under two specialized cases.

Of the DNA that you have, one-half of it came from your mother and one-half of it came from
your father. In turn, each of your parents inherited one-half of their DNA from their
parents. Thus, you have 1/2 of your parents DNA, or 1/4 of each of your grandparents, or
1/8 of each of your great grandparents, and so on. With a distant ancestor, the problem
would be identifying that fraction of your DNA that was handed down from the ancestor. In
virtually all cases, this would be impossible to do.

The two special exceptions are as follows:

A strictly paternal lineage could be shown, that is, your fathers fathers fathers........
The reason for this is that the Y chromosome is transmitted from father to son. Thus, your
Y chromosome is identical to your fathers, and to his fathers, and so on. The recent
conformation of Thomas Jefferson being the father of one of Sally Heming's children was
shown this way, the Y chromosome DNA of a male line from one of Sally's sons was shown to
be identical to the Y chromosome DNA from a male line from Thomas Jefferson's father, since
Thomas himself had no sons (or surviving male lines, I can't remember which it is). Notice
that in this case, there was no test of the DNA of Thomas Jefferson himself.

The second case involves a strictly maternal lineage, that is, your mothers mothers
mothers.......... There is a special type of DNA called mitochondrial DNA that is
inherited strictly from mother to offspring. Thus, you have your mothers mothers mothers
........ mitochondrial DNA. This was the type of testing that was done to identify the
remains of the Russian Romonov family.

So, with these two exceptions, any attempt to show lineage by DNA typing is essentially
impossible because of the mixing that occurs with each generation. Current tests usually
can show close relationships (parent - offspring, or siblings), but beyond that, it becomes
virtually impossible.

Additionally, DNA tests like this are not cheap, at least, not yet.

Still, your idea was an interesting one, perhaps in the future we will develop the
technology and databases to make this possible, but for now, it is not feasible.

Dick
--
~~~~~~~~~~~~~~~~~~~
Richard C. Gethmann


..... when you have eliminated the impossible, whatever remains,
however improbable, must be the truth..... A. Conan Doyle

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