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From: Gabriela Novak <>
Subject: Re: [DNA] Response to genetic genealogists from authors of Oct.19thScience ...
Date: Sat, 20 Oct 2007 13:59:00 -0400
References: <AAF331E1-12E7-48CB-BAB1-CC4CE8C572B5@mac.com>
In-Reply-To: <AAF331E1-12E7-48CB-BAB1-CC4CE8C572B5@mac.com>


> accept your neighbor. There is another way - celebrate diversity. It
> is that diversity that unites us, in a very literal sense. Diversity
> is the end result of our genome's quest for eternal life. No,
> individuals do not live forever, but we are all the end result of
> countless generations of adaptation.

If there is anyhing I have learned in my population genetics course,
it is:

1. variation is our strength, without it species perish
Example- a strain of highly productive wheat was generated and sold
to farmers, who planted these plants, which came from one predecessor
and hence were genetically identical, lacking genetic variability. A
disaster struck when whole fields were wiped out by one disease. This
did not happen to farmers who did not have the extra money to buy
this special seed and planted the ordinary, genetically varied,
species. Those fields contained plants taht happened to be resistant
to that disease. The same can happen to humans. We all have different
resistance to different diseases. 10% of northern Europeans carry a
gene variant making them resistant to AIDS (in the past this variant
was seleted for because it conferred resistance to another disease).
High percentage of Europeans carry the cystic fibrosis gene because
individuals carrying one copy of this gene are resistant to typhoid
and other diseases causing diarrhoea, such as cholera.

See Wikipedia - http://en.wikipedia.org/wiki/Cystic_fibrosis
Theories about the prevalence of CF:
The ΔF508 mutation is estimated to be up to 52,000 years old.[56]
Numerous hypotheses have been advanced as to why such a lethal
mutation has persisted and spread in the human population. Other
common autosomal recessive diseases such as sickle cell anemia have
been found to protect carriers from other diseases, a concept known
as heterozygote advantage. Resistance to the following have all been
proposed as possible sources of heterozygote advantage:
* Cholera: With the discovery that cholera toxin requires normal
host CFTR proteins to function properly, it was hypothesized that
carriers of mutant CFTR genes benefited from resistance to cholera
and other causes of diarrhea.[57] Further studies have not confirmed
this hypothesis.[58][59]
* Typhoid: Normal CFTR proteins are also essential for the entry
of Salmonella typhi into cells,[60] suggesting that carriers of
mutant CFTR genes might be resistant to typhoid fever. No in vivo
study has yet confirmed this. In both cases, the low level of cystic
fibrosis outside of Europe, in places where both cholera and typhoid
fever are endemic, is not immediately explicable.
* Diarrhoea: It has also been hypothesized that the prevalence
of CF in Europe might be connected with the development of cattle
domestication. In this hypothesis, carriers of a single mutant CFTR
chromosome had some protection from diarrhoea caused by lactose
intolerance, prior to the appearance of the mutations that created
lactose tolerance.[61]
* Tuberculosis: Poolman and Galvani from Yale University have
added another possible explanation - that carriers of the gene have
some resistance to TB.[62][63]


2. There is more variation within a population than between
populations. We differ more from one another within a population (or
race, if you prefer), than we differ from population to population.
There is less variation within our species than within most other
species. Two groups of monkeys of the same species living in the same
forest tend to be more different from each other than two humans from
opposite ends of the planet.

This is what population genetics is teaching us, not the opposite.
Unfortunately, as with anything, knowledge can always be twisted into
something bad, but you can't blame knowledge for that. We can only
see through such efforts if we educate ourselves. If we choose to
stay blind, we make ourselves easy targets to the ones who gain from
misusing others.

Gabriela


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