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Archiver > GENEALOGY-DNA > 2002-09 > 1031238389
From:
Subject: Re: [DNA] mtDNA - why just C and T substitutions?
Date: Thu, 5 Sep 2002 11:06:29 EDT
In a message dated 09/04/02 10:37:50 PM Pacific Daylight Time,
writes:
> I was looking at the CRS chart on the Cambridge site and the list of
> substitutions that comprise the other European clans -- why are the
> substitutions only C and T? Why not A or G? Does anyone have a theory?
Mutations to A and G do occur -- in fact, I'm 16293[G] -- but C<->T mutations
are indeed the most common.
The bases Cytosine and Thymosine have similar structures (they are both
pyrimidines), and Guanine and Adenine have similar structures (they are both
purines).
The great majority of mutations are "transitions," where one pyrimidine or
purine is substituted for the other. It's as if similar structures can fool
the replicating enzymes. "Transversions," where one purine is substituted for
a pyrimidine or vice versa, occur at a much lower rate.
But even just looking at the possible transitions, C/T and G/A. Guanine and
Adenine have a more complex structure, so maybe that makes it even harder to
fool the replicating enzymes.
For diagrams of the chemical structures, see
http://www.ncbi.nlm.nih.gov/books/bv.fcgi?call=bv.View..ShowSection&;
rid=iga.figgrp.d1e32524
Ann Turner
GENEALOGY-DNA List Administrator
http://lists.rootsweb.com/index/other/Miscellaneous/GENEALOGY-DNA.html
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