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Same gene, different GC%...

Warren Gallin wgallin at gpu.srv.ualberta.ca
Mon Aug 14 11:12:20 EST 1995

In Article <u58563-1308950129000001 at genetics.comd.uic.edu>, u58563 at uic.edu
(Tommy the Terrorist) wrote:
>I've been involved with a project in which the human form of a gene is 50% GC,
and the mouse form is 60%.  The coding sequence is only about 80% conserved
on protein and DNA levels; the changes are primarily GC ---> AT transitions.
Interestingly, about 75% of the CpG doublets in the mouse have been lost
from the human (but almost all of the human CG's are present in the mouse). 
Nevertheless, the other transitions are predominantly in the same direction.

Do you have some reason for thinking that the mouse geen is more
representative of the ancestral form than the human is?  Why not that the
mouse has acquired more CpG doublets?

>   Thus, we have a pair of homologues, one of which seems to differ from the
other primarily due to (I presume) methylcytosine formation and conversion
to thymine.  It would appear to be a case in which evolution is driven
neither by natural selection nor in a strictly random fashion.

I don't think you can make that case without looking at the homologue in
more species than just two.

Warren Gallin,
Department of Biological Sciences, University of Alberta
wgallin at gpu.srv.ualberta.ca

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