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FW: Radiation Hormesis -- or not
John Jacobus and Catherine Perham wrote:
-----Original Message-----
From: John Jacobus [mailto:crispy_bird@YAHOO.COM]
Sent: Tuesday, January 27, 2004 6:21 AM
To: Catherine Perham
Cc: 'radsafe@list.Vanderbilt.Edu'
Subject: RE: Radiation Hormesis -- or not
Catherine
I would also say that not all negative mutations are
selected against survival. There are a number of
genetic diseases that do not improve the species, e.g.
hemophilia, but are still present and are passed
along. It escapes me what was the evolutionary or
genetic process that allowed it to exist in humans.
--- Catherine Perham <cperham@ehso.emory.edu> wrote:
> John;
>
> Genetic effects are completely random and as you
> mention cannot be "willed."
> We only see the positive genetic mutations such as
> opposable thumbs because
> all of the negative mutations were selected against-
> in other words, they
> died. Random effects are very unlikely to be
> positive and that is why
> evolution takes so long. Most mutations change a
> protein structure such as
> a hormone that may render it unusable to the
> organism.
====================
Another subscriber noted that natural selection will only operate against features that affect reproductive success. Thus, natural selection does not select against cancers with average onset in old age. Someone else noted that hemophilia could persist because it was sex-linked with an unaffected population (female) of carriers.
There is another phenomenon that allows some genetic diseases that are recessive and fatal to homozygous individuals to persist, even though the homozygous normally die without reproducing. Sickle cell anemia is a good example; it persists in a number of tropical and sub-tropical populations because heterozygous carriers of the mutated gene have substantially less susceptibility to malaria. There is a similar situation with the gene for one of the fatal recessive diseases of Ashkenazy Jews -- Tay-Sachs, if memory serves. T-S heterozygotes appear to have less susceptibility to tuberculosis, an important disease of the urban ghettos that were home to most Ashkenazim. Some geneticists speculate that for all fatal recessive genetic diseases, the heterozygotes have to have some survival advantage for the disease to persist in a population at anything about random mutation levels.
Best regards.
Jim Dukelow
Pacific Northwest National Laboratory
Richland, WA
jim.dukelow@pnl.gov
These comments are mine and have not been reviewed and/or approved by my management or the U.S. Department of Energy.
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