Humans >99% identical to chimps in noncoding DNA

Brian Foley btf at lanl.gov
Wed Nov 24 19:40:54 EST 1999


There are a couple of recent papers reporting 
sequencing of over 10 Kb of non-coding DNA from the
X chromosome of 30 different chimps (representing
Pan troglodytes troglodytes, Pan troglodytes 
schweinfurthii, Pan troglodytes verus and Pan paniscus)
a lowland gorilla, an orangutan, and 69 humans from
all over the world (including native north and
south Americans, Australian aborigines, etc...).
See Kaessmann et al Science 286: 1159-1162 (1999)
and Kaessmann et al Nature Genetics 22: 78 (1999)
and the GenBank entries with accession numbers
AJ270061-AJ270095, AJ241023-AJ241093 which are the
raw data.

	Anyway, I found it a bit surprising that this
10Kb of non-coding DNA was so highly conserved.  It
seems it mutates about 30 times slower than primate
mitochondrial DNA.  If it is representative of nulcear
DNA, it shows that humans are more than 99% identical to
chimpanzees at the nucleotide level, and thus likely
to be much more than 99% identical to chimpanzees at
the amino acid sequence level (because many mutations
are silent).

	Also noted, is that human genetic diversity is
far less than chimpanzee genetic diversity.  Apparently 
humans went through a genetic bottleneck and we are
all descended from a small population not too long ago.  It's
funny how people think all these "races" of humans mean we have
a lot of diversity and all chimps look alike to us so we assume
they are less diverse.  It just isn't true.  I'm not sure if I'm 
reading this figure right, but it seems to say they found a much
higher mutation rate in the mitochondiral DNA, than in the
X chromosome DNA, like 30 times as much variability in mt-DNA
as in X chromosome non-coding DNA.  That's a bit surprising,
but maybe the different polymerase and repair enzymes do make that
much difference.  Not to mention that the mitochondrial DNA 
might have a lot of oxidative stress there in the powerhouse of
the cell.
	It seems you can rest assured that whatever 
human they used for the human genome program the story is pretty
much "If you've seen one human, you've seen 'em all."  The
MHC and other loci that make us unique will be the exceptions
to that general rule.

-- 
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|Brian T. Foley               btf at t10.lanl.gov                 |
|HIV Database                 (505) 665-1970                   |
|Los Alamos National Lab      http://hiv-web.lanl.gov/         |
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