genetic markers

[Vidyasankar Sundaresan]

Raoul Martens <raoul at MARTENS.PP.SE> wrote:

>The NATURE issue of Dec. 7, 2000 has three articles about population
>genetics where mitochondrial DNA only was applied as genetic marker.
.....
>2. Mitochondrial genome variations and the origine of modern humans
>by Max Ingman, Henrik Kaessmann, Svante Pääbo & Ulf Gyllensten

This is a very important research work about human populations.
Three interesting points, in relation to the issues discussed
on this list recently -

The authors do not agree with the theory of Awadalla et al
(Science, 286 (5449): 2524-2525.), that mitochondrial DNA may
undergo recombination. They also show how X chromosome data do
not correlate exactly with their data in details, but still
lead to the same overall conclusions regarding the origins of
the modern human species, Homo Sapiens, in Africa.

The sample studied consists of 53 individuals from the entire
planet, chosen to represent the major linguistic phyla in the
world, and corrected for biases introduced by contemporary
demographics. The linguists on this list may find the figure
of the phylogenetic tree very interesting. It should also be
evident that very useful information can be obtained even out
of small sample sizes. My feeling is that using larger sample
sizes will surely add finer detail, but the overall conclusions
drawn in these kinds of studies will remain valid. Genetic
studies hold enormous potential for understanding population
movements, so long as scientifically valid questions are asked
and the right kinds of tests are correspondingly designed.

The time scale obtained from the "genetic clock" ranges from
171,000 plus or minus 50,000 years ago (upper bound) and 52,000
plus or minus 27,500 years ago (lower bound). Notice where the
data are centered and also how the error bars span 25% to 50%
of the mean values.

Vidyasankar

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