RE: Genetic Effects?

["Bjorn Cedervall" <bcradsafers@HOTMAIL.COM>]

>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.



I never questioned any of that.



1. I definitely believe that ionizing radiation can be the cause of point 

mutations or chromosomal rearrangements (I have H. Muller's paper from 1927 

about X-rays and mutations in Drosophila by the way).

2. I also definitely believe that these changes can reach the fertilized egg 

as well as the ultimate individual.

3. I also believe that some mutations reach the population level but it is 

probably very hard to detect for most genes (the human species' gene pool 

probably mutates with an average of dozens of beneficial mutations every 

single year - the frequency of negative mutations are probably at least 1000 

billion times higher than that - I am interested in any references or solid 

reasoning casting more light upon this aspect).



My point is about the strong _statistical_ selection pressure against most 

alleles (mutated genes) that create a much lowered probability of survival 

for each individual carrying such specific alleles. A mutation can never be 

good or bad - it must have a genetic context (all other genetic material in 

that same individual) as well as environmental context (first pointed out by 

Dobzhansky around 1937). Some alleles with a negative fitness (after 

embryonal stage and with relatively high penetrance as expressed) reach the 

adult stage relatively easily.



I am interested in any statistically solid references showing that exposure 

to ionizing radiation of humans caused mutations in the germ line that were 

_expressed_ on a phenotype level in next generations.





>there is ample evidence that the human system will produce noncompetitive 

>individuals repeatedly



I agree but one problem (all is not about point mutations) is to sort out if 

the major cause may have been a recessive gene (negative fitness) that was 

created 10 000 years ago and just by chance ended up in the wrong genetic 

context (like for instance another homologous recessive gene - caused by 

some particluar agent in the previous generation). To show this solid 

statistics is necessary.





>occur. the references to dobzan, crow etc  are basically detailed math 

>theory and refer to population genetics.



Dobzhansky was an experimentalist testing the mathematics theory. Crow's 

PNAS paper I referred to: Just read it and lets discuss the details rather 

than just refer to it as "math theory" (very little of equation stuff in it 

- lots of thoughtful reading)! I have read six of Ernst Mayr's (I referred 

to him as well) books on evolution and the species - never saw an equation 

in any of his books. GL Stebbins was not a math theory person either. What 

they, and GG Simpson (paleontologist) did was to bring together what could 

be observed in nature or in experiments with what the math people (Fisher, 

Haldane, Wright and a few others) came up with. This created a synthetic 

understanding for the evolutionary theory (still being developed). I agree 

that Crow and Kimura as well as some other recent workers did a lot of work 

along the mathematical line - in particular the works on the "neutral 

theory" by Kimura may be worth some reading (there was an article about that 

in Scientific American - may be more than 20 years ago - must be easy to 

find with Google).



>  pick up any medical genetics book and the genetics are clear for fimilial 

>transfer through sexual reproduction.

I am not questioning any of that. My question is stricltly about mutations 

caused by exposure to "mancreated" ionizing radiation and to what degree 

that can be seen in future generations of humans.





>the paramecia do not actually have 36 sexes,



It was 34 but I should have written "34 possible sexes" (or 33 possible 

opposite sexes) - besides the mathematical comment it was a joke which I 

indicated with a :-).

Sorry about that. I keep my original writing at the end of this message.

There are about 28000 possible mating partners for Schizophyllum commune 

(split-gilled mushroom) determined by two loci with more than 90 and more 

than 300 respectively.

Some organisms switch between sexual and asexual production - lots to read 

there with or without math.





 >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."



Yes - but notice the word "CAN" in the last line. What does that mean in 

terms of probabilities related to the next generation? The load we already 

carry is typically much larger than anything you can induce on the level of 

the individual. The only way to see it should reasonably be statistical on 

_very large_ populations. I ask whether this has been detected on a 

phenotype level in humans. If there are such references I want to read them 

ASAP.



I give the evolution links & references again - the people I point at stood 

for much of the important delevopment of the evolutionary theory during the 

past century.



Finally, it may be of interest that the ICRP now - in its draft for new 

recommendations - suggest lowering the weighting for gonads by 75 %.



My personal thoughts and ideas only,



Bjorn Cedervall     bcradsafers@hotmail.com

http://www.geocities.com/bjorn_cedervall/Science/evolution_links.html

------------------------------------------------------------------------------------------------------------------

>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 :-).





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