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RE: Genetic Effects?
as a molecular geneticist, there is clearly no question that the transfer can take place. there is a wealth of point mutation evidence in familial mating trees etc.
honestly speaking, sometimes it is difficult to determine if the writer is questioning ionizing radiation effects on dna or ability to reach the sperm/egg dna or is expressing no belief in the genetic transfer mechanism.
defective eggs, sperms and embryos that we never see do not not show up because of natural selection but just basically deffective in the replication,division or differention stages that first contribute to simple cell devision to support life period, regardless of selective pressure or natural selection. these cells have already met that standard; in other words human cells do not go through testing cell devision basics each time they are triggered to divide. if the tried and true basics are not there they do not divide regardless of the pressure to divide, replicate and differentiate. these are the types of mutations that cause most of the first trimester abortions or spontaneous abortions. there is ample evidence that the human system will produce noncompetitive individuals repeatedly and what we do is modify the environment so that natural selection(interaction with the environment) will not eleminate them.
from what i have read, it appears that most have a molecular question not a populational one that we drifted into to explain why such mutation have not accumulated in the gene pool if they do occur. the references to dobzan, crow etc are basically detailed math theory and refer to population genetics. the possible causes are not investigated but simply mentioned. those papers discuss the dynamics of the gene pool. pick up any medical genetics book and the genetics are clear for fimilial transfer through sexual reproduction.
the paramecia do not actually have 36 sexes, in fact there are some interesting genetic papers as to whether humans have only one sex and the other is a mutational change which boils down to an interesting discussion on gene expression. however, these are really referred to as mating types rather than sexes(baker's yeast offeres the most definitive studies on this) for purposes of discussion they are referred to as male and female sometimes. incidentally, those mating types are influenced by environment/nutrition for yeast and other single cellers.
-----Original Message-----
From: owner-radsafe@list.vanderbilt.edu
[mailto:owner-radsafe@list.vanderbilt.edu]On Behalf Of Bjorn Cedervall
Sent: Wednesday, November 17, 2004 1:38 AM
To: radsafe@list.vanderbilt.edu
Subject: Re: Genetic Effects?
>The Sep. 2004 issue of Science & Technology Review from LLNL includes a
>primer on radiation in a sidebar on p. 6. In it, the following statement
>is made: "Exposure to large amounts of ionizing radiation (on the order of
>hundreds of times the natural exposure levels) increases the risk of. . .
>genetic mutations that can be passed on to future generations."
>
>Is there any evidence of this (genetic effects) in humans?
-----
Of course they can be passed on to future generations - in theory.
However, it is questionable whether this can be an important problem since
there is strong selection against any damage on a DNA-level that is severe
(regardless of its cause) at the germ cell stage, and early embryos.
Therefore, what will be missed by these natural selection processes will
reasonably be:
1/ Mutations which play no or small roles during embryogenesis / fetal
development.
2/ Mutations which will have minor effects on the fitness of the individual
(each one of us may carry many such mutations).
Among the most important factors that damage our genome on a population
level (all members of the species defined as the common gene pool) is modern
medicine. This is ethically an impossible situation because we all want our
loved ones to survive but nature is brutal and has created a conflict
between the interest of the individual (and its closest relatives) and that
of the population (if the population could have "an interest" - here just
meant to refer to future overall survival). For sexually reproducing species
(with two sexes) an average of 2 (long term) offspring should survive. We
set that number 2 aside (population growth) and along with that probably
increased vulnerability in the future.
I have collected some evolutionary biology links here:
http://www.geocities.com/bjorn_cedervall/Science/evolution_links.html
(I came across tons of anti-evolution sites while going through this stuff
- tons of scary misinterpretations: One of the worst is that selection is
against
something rather than for (because selection cannot have a positive
purpose)).
Suggested start:
The high spontaneous mutation rate: Is it a health risk?, PNAS, Vol. 94,
1997:8380-8386.
For species with more than two sexes the math must be extremely complex -
Paramecia have 34 different sexes (one opposite sex may be complicated
enough - even without math :-).
I have simplified some reasoning above but believe that the essence is OK.
Please add, subtract or modify whatever may be necessary. For more about
"species" I refer to Ernst Mayr, Stebbins and Dobzhansky as first basic
stuff - there is a lot of other quality reading out there (Crow and Kimura
for instance).
My personal action and ideas only,
Bjorn Cedervall bcradsafers@hotmail.com
http://www.geocities.com/bjorn_cedervall/
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