In article <9205142126.AA06934 at genbank.bio.net>
dac at sci.ccny.cuny.edu (David A Cooke)
> As I have posted before, spontaneous abortion provides a very
> effective quality-control process that does not require rewriting of
> DNA by some magical repair mechanism.
First of all, recombinatorial DNA repair is a reasonably well
understood mechanism documented in the text "Aging, Sex, and
DNA Repair" by Bernstein and Bernstein. It is a fact and not "some
magical repair mechanism". Secondly, as I have posted before,
spontaneous abortion is not a sufficient mechanism to explain
why children start life with a clean slate of DNA. There are
other mechanisms, such as recombinatorial DNA repair that also
play a role.
>> (1) Resistance to a DNA-damaging agent is considerably greater
>> when two chromosomes are present than when just one is
>> present. (2) This resistance is diminished by mutations
>> in genes required for recombination. (3) DNA damaging
>> agents increase recombination. (4) Mutants defective in
>> repair pathways other than recombinational repair have
>> increased levels of recombinations.
>> The reason for increased resistance to DNA damage when two chromosomes
> are present does not have to have anything to do with a repair mechanism.
> It is based on the fact that in most cases, only one functional gene is
> necessary for normal gene product expression and function.
Your statement is at odds with observations 2, 3 and 4 above. Whether
or not error correction plays an important role in observation 1 can
only be determined by a careful analysis of the data (sorry I
don't have access to it).
>> Provisioning the eggs with metabolic products to be used by the
>> developing embryo involves considerable metabolic activity,
>> which produces oxidative free radicals as by-products. These,
>> in turn, would cause DNA damage. Thus, the common strategy
>> of provisioning the egg may increase DNA damage and as a
>> result may increase the need for DNA repair. Consequently there
>> is a special adaptive value of meiotic DNA repair during
>> oogenesis.
>> Perhaps, but there are plenty of other good reasons for giving
> a developing embryo lots of food to start with (e.g. nutrient acquisition
> would be a big problem at that stage of life).
Of course there are other reasons for provisioning the egg, but you
seem to have missed the point! The point is that DNA contained in
eggs is exposed to a high level of free oxygen radicals and as a result
a high level of errors may be introduced into the DNA.
