[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Population genetics for Joe



Hi Dale,
You are going from humorous to just overbearing and a little bizarre.
The I am well aware of the effect called xenia  and the cross section
of  corn seeds as well as  the seeds of a number of other grains and
crops such as coconut. Nobody, but you,  would be willing to say that
the endosperm  contribution  was insignificant  in the pollution of
transgenic seed crops. However, I think you cannot avoid the main point:
transgenic pollution  by pollen is expressed the very generation of
pollen spread. A note on xenia below.
Sincerely, Prof. Joe Cummins

Kiesselback, T.A. 1980. The Structure and Reproduction of Corn.
University of Nebraska Free Press. Lincoln, Nebraska. (pg 85-86).

Xenia - Kiesselback stated that:

"all effects of foreign pollen which appeared in fruit, seed, or
vegetative structure of the female parent. Any change in the tissue of
the mother plant, such as a change in weight or size of pericarp, is now
called metaxenia. Change in embryo tissue, as in the color or
composition of the cotyledons of peas, is not generally regarded as
xenia, so that use of the term is now usually limited to any changes in
endosperm resulting as an immediate effect of foreign pollen.

Xenia is common in corn, especially by way of aleurone - and endosperm -
color responses and changes in the composition, texture, and weight of
the endosperm. For example, the kernels of white sweet corn become
yellow, starchy, and heavier when outcrossed by plants with yellow
starchy kernels.

Xenia is very convenient in the demonstration of segregation, as the
kernels can be counted, where as most sporophytic responses are not
apparent until the seed is planted and the character becomes visible in
the progeny plants."

Xenia - the direct effect of pollen genotype on the endosperm, which
includes the aleurone layer.


       Example:

In maize, due to double fertilization of embryo and endosperm tissue,
the alleles carried by the pollen parent may be manifested on the
endosperm tissue.

(Rr of the male) x (rr of the female) results in:

1/2 Rrr (purple aleurone)
1/2 rrr (yellow aleurone)

(rr of the male) x (rr of the female) results in - rrr, all yellow aleurone.

The effect of the pollen genotype is immediately evident.



Dale Wilson wrote:

Joe,



Regarding the most significant point double fertilization you seem to
be misunderstanding or just obfuscating the main point. In single
fertilizations or plants with little or no endosperm  the transgenic
portion of  the seed is limited to an immature embryo making up a
minute portion of the seed.



Single or double fertilization, if the ovule is fertilized with a
pollen grain containing a transgene, the whole embryo is transgenic.
In a soybean, for example, the embryo constitutes pretty much the whole
seed (now, this may be a moot point for soybean because generally the
flower is self-pollinated before opening).

In corn, the embryo (including the scutellum) is very large, making up
a substantial fraction of the kernel.  In any case, if the corn ovule
is fertilized by a transgenic pollen grain, both the embryo and the
endosperm will be transgenic.  The plant that arises from the kernel
will be transgenic, and if the kernel is tested, it will test
transgenic.



The GM plant with every cell containing
transgenes will not appear until the following  season of growth of
the seed.



Except for the pericarp (hull) every cell in a kernel of corn arising
from a transgenic pollen grain that landed on a conventional
(nontransgenic) corn plant, will be transgenic.  It is transgenic
through and through.  Double fertilization is beside the point.



In
grain of the endosperm rich crops  a large portion of  the seed is
triploid endosperm containing  transgenic cells. So in the  crops
lacking endosperm  the GM content of the  crop is heavily laden with
transgenic material in the generation of the fertilization.



Well, yeah.  And that is also the case in endospermic seeds.
Endospermic or non-endospermic, a seed fertilized by a transgenic
pollen grain will be transgenic through and through.

Joe, I don't understand what we are disagreeing about.  I don't think
we are genuinely disagreeing about anything.  Nothing of substance
anyhow.



The point you  made about GM detection in kernels is strange to say
the least.



It is important if you are trying to sell grain into a market that
demands a certain maximum GMO contamination level.



The food
standards for GM content are not set for  number of transgenic
kernels but for transgene content in the food!



If 5% of the kernels are transgenic, then the tortillas you make from
it are made from 5% trangenic corn.  This doesn't seem very
complicated.



Again  it is very unwise to
pretend that transgenic endosperm does not count in grain crops!



This is some sort of straw man argument you have cooked up.  I am not
claiming that at all.

Farmers selling into markets that demand non-GMO corn need to look at
this on the basis of fraction of kernels contaminated.  This is not
only the simplest way to look at the problem, it relates directly to
how seed and grain is tested.

Dale

__________________________________
Do you Yahoo!?
Yahoo! SiteBuilder - Free, easy-to-use web site design software
http://sitebuilder.yahoo.com

********************************************************

To unsubscribe from SANET-MG:
1- Visit http://lists.sare.org/archives/sanet-mg.html and unsubscribe by typing in your e-mail address or;
2- Send a message to <listserv@sare.org> from the address subscribed to the list. Type "unsubscribe sanet-mg" in the body of the message.

Visit the SANET-MG archives at: http://lists.sare.org/archives/sanet-mg.html



********************************************************

To unsubscribe from SANET-MG:
1- Visit http://lists.sare.org/archives/sanet-mg.html and unsubscribe by typing in your e-mail address or;
2- Send a message to <listserv@sare.org> from the address subscribed to the list. Type "unsubscribe sanet-mg" in the body of the message.

Visit the SANET-MG archives at: http://lists.sare.org/archives/sanet-mg.html