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Re: Marcotrigiano not good enough?


>Marcotrigino shows mit rec it suddenly is not important He 
>shows a twinspot ie 2 adjacent spots, a green and a white one If 
>you would have know anything about the subject you had 
>recognized that such a twinspot is a classical proof for mit rec.

Twin spots can also arise from chromosome loss.  Given the high doses 
or iriadation that are needed to develop conditions that suggest 
mitotic recombination, it it just as likely, maybe more so that what 
you see is the result of irriadiation induced chromosome damage.  If 
you want to prove it is mitotic recombination and not chromosome loss 
then you have to do genetic analysis of the resulting twin spots.  
Difficult to do when it is only a very tiny spot on a leaf surface.

Now, Ben, no one is claiming that mitotic recombination does not take 
place in higher plants.  All we are saying is that the rate of mitotic 
recombination is so LOW that it is not a factor in explaining green 
edges showing up on yellow hostas.  If you think mitotic recombination 
is the cause for this, then prove it.  If you look at all the 
experiments where twin spots were developed that indicate that mitotic 
recombination occure you will see that these are SMALL spots on a leaf 
surface - a far cry away from resulting in a variegated plant.  I 
don't know how many millions of cells a tobacco plant has, certainly 
in the tens if not hundreds of millions.  After growing out hundreds 
of plants that were heavily irriadated they could only come up with 
one small spot to indicate mitotic recopbination, and still couldn't 
prove it.  The problem you are failing to understand Ben is that if a 
mitotic recombination were to take place that resulted in a L1-L2 
layer green-yellow chimera, it would have to occure in the apical 
meristem cells to form a periclinial chimera or in one of the daughter 
cells of the apical meristem cells to form a mericlinal chimera that 
could then be convered to a periclinal chimera.  You are not only 
taking about an event occuring that has a VERY low chance of occuring, 
without irriadiation maybe in the order of 1 in ten billion cell 
divisions, AND that mitotic recombination has to take place in the 
shoot apex.  You are just asking for too much.

Now, irriadiation is well known to cause chomosome damage.  It seems 
very lofgical to me that when you treat a plant with high doses of 
radiation that any spots that develop that appear to be the expression 
of a gene where you wouldn't expect that expression is the result of 
chromosome damage due to irriadiation.  If you think I am wrong, then 
PROVE that mitotic recombination is the cause.  We have two equally 
plausible explinations for a given event.  We both can't be right, 
although we can both be wrong.  Until such time as you can PROVE 
otherwise I say I am correct!

Joe Halinar

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