🚀 go-pugleaf

In article <1993Jan21.041055.24779@organpipe.uug.arizona.edu> sfm@manduca.neurobio.arizona.edu (Stephen Matheson) writes:
>From article <105875@netnews.upenn.edu>,
>by barkdoll@lepomis.psych.upenn.edu (spacesareforthefeebleminded):
>> In article <1759@tdat.teradata.COM> swf@tools3teradata.com
>> (Stan Friesen) writes:
>>>In article <104941@netnews.upenn.edu>,
>>>rowe@pender.ee.upenn.edu (Mickey Rowe) writes:
>
>>>|> >The brain statement is based on the fact that neurons have less
>>>|> >DNA per unit weight than other kinds of cells (eggs-cluding eggs
>>>|> >and who knows what other special cases).  
>
>>>|> I suspect that this is generally untrue.
>
>>>Ah, but it is in fact exactly literally true!  All cells in a single
>>>body have the *same* amount of DNA (with a few wierd exception like
>>>the polytene chromosomes in the salivary glands of Drosophila).
>
>> 	Ah, but it is in fact exactly literally false!  Class
>> switching of B cells, antigen specificity selection of immunoglobulins
>> and T cell receptor specifity all involve deletion and recombination
>> of DNA.  Then of course most ("most" is just to hedge my bets) mature
>> mammalian red blood cells have NO nuclear DNA.
>
>First of all, I would argue that both your examples might be classified
>as "weird exceptions".

	Given that the number of neurons claimed to be in the human
brain is ~10^11 and the number of RBC's in the average male is about
10^13, together with the fact that marsupials, monotremes and
eutherian mammals have anucleate RBC's, I suggest that you have an odd
sense of what is a "weird exceptino".  Ditto for B and T cells.
Although the numbers in a normal individual are lower - say a
mere 10^10 - they are ubiquitous in mammals, birds and possibly
reptiles, amphibians and fish (not sure about the last three).

>More importantly, I am skeptical that the
>DNA rearrangements you refer to could have any measureable effect on
>the rather crude DNA-per-unit-weight measurement.

	Obviously.  That was not my point regarding B and T cells,
rather I took exception to Stanley's strong statement above.

-- 
Edwin Barkdoll
eb3@world.std.com