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Archiver > GENEALOGY-DNA > 2002-03 > 1015119703


From: "Allan S. Gleason" <>
Subject: Re: [DNA] Results Comments?
Date: Sat, 02 Mar 2002 18:41:43 -0700
References: <JCHBN.020302.165226.RC0@CUVMB.CC.COLUMBIA.EDU>


Sorry, John. I simply misread what you said - guess I'm getting older than I
thought I was getting.

As a matter of fact, Huntington's mutation is an example of the effect of
increasing short term mutation of genes in chromosome 4. There are stretches of CAG
which tend to mutate because the counting mechanism in the gene during replication
seems to miscount and the regions become longer and longer. This happens at every
division of the cell so that as the male sperm regenerates these regions become
longer. Thus the older the father at conception the sooner the onset of the disease
in the children. It appears that an examination of that gene and a count of the
repeats is so accurate that they can predict virtually the exact life expectancy of
the child.

It is incredible story about a horrible disease but the subject is discussed in
great detail in the book Genome by Matt Ridley. (I've mentioned this fabulous book
before)

Allan

"John F. Chandler" wrote:

> I wrote:
> > mutation mechanism for STR markers were strongly biased in favor of
> > *increasing* the repeat counts, then it could be said that a value of
> > 20 for DYS390 is more "ancient" than a value of 24, but that is not
> > established.
>
> Allan asked for an explanation. It has been suggested more than once
> that STR mutations are preferentially an increase in the number of
> repeats, rather than a decrease. However, no one has published any
> definitive study to show whether this idea is true or false. If I
> remember correctly, the report on father-son differences did have an
> excess of increases over decreases, but the statistics were too few
> to make anything of that.
>
> John Chandler
>
> ==============================
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