🚀 go-pugleaf

Peter Ashby <p-ashby@nimr.MAPS.mrc.ac.uk> wrote (�crivait)�:

> ...(snip) .........I said that the disappearance can be easily
> *accounted for* that is an entirely different thing. The disappearance
> takes time obviously, although selective death on a voyage could EASILY do
> the same thing quite quickly.
> .....(snip)...

Although not a specialist of population dynamics, it sounds as an
interesting argument. When very few people established somewhere, often
after many deadly tries across huge distances, they could represent a
peculiar sampling of the starting population, just as my own family is
not representative of the average genetic features of my country. Some
genes may have been selected by chance. I have read in the past that
population tracing by use of blood groups is not quite reliable if not
done together with other techniques, such as mtDNA sequencing.

The molecular difference between the determinants of A and B groups is
tiny. In the Y-shaped surface polysaccharides of red cells, one of the
branch has a N-acetylgalactosamine unit (A), or a galactose (B). The
difference in A and B specificity appears to reside ultimately in a
relatively small structural variation, namely in the substituent at C-2
in a sugar with a galactose configuration (sorry for this chemical
detail). The assembly of sugar units in polysaccharides is controlled by
the speciificity of enzymes that catalyse the binding with a very strict
orientation. Mutations occurring by chance can modify the specificity of
the enzymes (or suppress it), so a different sugar is installed. The
same changes can occur in a population at different times and be
unrelated. This may blurr the tracing of events.

Probably blood group statistics must be used with extreme care before
conclusions be drawn about human migratory events, but I am aware that
other facts I do not know may exist and contradict this. Sincerely   

-- 
J. Pelmont, Biochimie
Univ. Grenoble I