david.machugh at ucd.ie
Tue Dec 7 11:55:17 EST 1999
It is not surprising that protein polymorphisms identified and characterised
in one species do not show the same level of variability in another species.
Most of the protein markers used would have been originally tested for
polymorphism in humans. However, just because they are variable in humans
doesn't mean they will be variable in related species. This introduces a
substantial ascertainment bias which can be removed by looking at variation
at the DNA level (preferably random non-coding segments and as much as
In addition, many of these markers were originally characterised and
developed in Caucasian European populations and this explains why previous
studies of allozyme variation in African populations uncover less
polymorphism than might be expected given the substantial DNA-level
variation in the same populations.
All of the DNA-based studies to-date (mitochondrial, autosomal and
sex-chromosomal) have found that humans, relative to other primates are
remarkably genetically homogenous.
By the way, you could recreate the same ascertainment problem with DNA by
only using DNA polymorphisms which had been found to be variable in humans
and then assaying them in chimpanzee populations. For example, most of the
random human single-nucleotide polymorphisms (SNPs) which are currently
being developed in great numbers, will be useless for studies of genetic
variation in chimpanzees.
David MacHugh, Ph.D.
Department of Animal Science and Production,
Faculty of Agriculture,
University College Dublin,
Email: david.machugh at ucd.ie
> From: Laurence Martin Cook <LCOOK at fs1.scg.man.ac.uk>
> Organization: BIOSCI International Newsgroups for Molecular Biology
> Date: Mon, 06 Dec 1999 12:15:32 -0800
> To: mol-evol at hgmp.mrc.ac.uk
> Subject: human/chimp identity
> A short while ago Brian Foley wrote that sequence data show the human
> genome to be very invariant, while chimpanzees are variable. It must
> depend where you look.
> Some years ago Eviatar nevo and collegues made a number of surveys of
> data from electrophoretically detectable protein studies of
> organisms. In the one I am looking at, there is for man a
> probability of 0.47 that a locus is polymorphic (for 107 loci in 7349
> individuals). Silent mutations will make this even higher at the
> DNA level, and it is not just systems like MHC which are involved.
> The equivalent figures for Pan are P=0.079 (42 loci in 182
> individuals). In the latter case only two populations were
> studied and it is possible variation between groups is great.
> "If you've seen one human, you've seen them all." Not on this
> evidence, you haven't. At the present time it seems necessary and
> interesting to review critically the evidence for variability coming
> from different types of investigation. Has this been done?
> Laurence M. Cook
> The Manchester Museum
> University of Manchester
> Manchester M13 9PL U.K.
> and:_lcook2 at excite.com
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