Lower-than-expected linkage disequilibrium

Andrew Gyles syzygium at alphalink.com.au
Sun Sep 9 21:57:58 EST 2001


"Gordon D. Pusch" <gdpusch at NO.xnet.SPAM.com> wrote in message
news:9nh3b5$5br$1 at mercury.hgmp.mrc.ac.uk...
> Andrew Gyles <syzygium at alphalink.com.au> writes:
>
> > My interest was in finding a mechanism that might have reduced sequence
> > variation in humans compared with apes. I thought that biased gene
> > conversion might have achieved this. However, one geneticist has told
> > me that the evidence for low sequence variation in humans is very weak;
> > if that is the case it does not have to be explained! But Steve Jones,
> > geneticist at University College, London, says that there is less
> > sequence variation between two human groups at each other's antipodes on
> > the planet than there is between two groups of chimpanzees living 20
> > miles apart in Africa, so I don't know what to accept.
>
> ISTR reading a news article in (IRRC) _Nature_ in the mid-to-late 1980's
> claiming that this reduced sequence variation can be most naturally
> understood as being the consequence of the human species suffering
> a near-extinction event in evolutionarily recent times, but prior
> to the migration out of Africa ???
>
>
> -- Gordon D. Pusch
>
> perl -e '$_ = "gdpusch\@NO.xnet.SPAM.com\n"; s/NO\.//; s/SPAM\.//; print;'
>
> ---
>
>
You probably recall reading one of various articles by Allan C Wilson et al
about low sequence variation in mtDNA in humans compared with chimpanzees.
The definitive article was published in 'Nature' in January, 1987.

Wilson's logic was that the low variation must have been caused by a
'bottleneck' in population size in Africa roughly 100,000 years ago (more
recent articles by other workers have reduced this to as recently as 50,000
years ago). Then they proposed various other 'bottlenecks' to explain the
low mtDNA variation in various human groups outside Africa.

Other workers have proposed a 'bottleneck' in the Neanderthal ancestors to
explain the low mtDNA variation found in three fossil Neanderthal bones (one
found in Germany and two found in, I think, Georgia).

I have been trying to find alternative explanations for the mtDNA data and
also for reported low sequence variation in nuclear chromosomes in humans.
The bottlenecks could explain the latter, but so could biased gene
conversion. I am not a specialist in genetics, so I have probably gone as
far as I can go.

Regards,

Andrew Gyles



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