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Re: Population genetics for Joe



I do not how it happened but  an important not was deleted from my eartlier  letter. Please regard this letter  to be the correct one.

joe cummins wrote:
Hi Dale,
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. The  GM plant with every cell containing transgenes will not appear until the following  season of growth of the seed. 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 not heavily laden with transgenic material in the generation of  the fertilization. If you do not understand that simple point it is not surprising that  agricultural bureaucrats often too ignore  plant biology.
The point you  made about GM detection in kernels is strange to say the least. The difference between  a seed with  no endosperm and a minute embryo  and a seed  rich in endosperm  may be as much as 100,000  to a million times  in number of transgenes in each kernel. The food standards for GM content are not set for  number of transgenic kernels but for transgene content in the food! Again  it is very unwise to pretend that  transgenic endosperm does not count in grain crops!
Most transgenes are dominant in _expression_ but homozygous  GM crops are not uncommon as are hemizygous crops, a point that  is not relevant to the discussion of endosperm. Keeping focused on endosperm , that tissue  contains one transgene , say, for every two normal genes but that ratio is offset by the huge production of endosperm relative to embryo. Of course, endosperm does not pass its genes to the next generation but it makes a huge impact on grain crops in the generation of fertilization.
The amplification of transgenes under selection is a separate story.
Thanks for your comments, dale, they are as always very amusing.
Sincerely, Joe

Dale Wilson wrote:
Joe,

  
I think that we should make it clear that the plants double
fertilization has an important impact. In plants the pollen
fertilizes both the egg cell and  the endosperm nucleus to produce
a triploid. So unlike the embryo whose _expression_ is delayed to the
next planting the endosperm  expresses the transgene  in the the
immediate generation  fertilized by  5 plants in each 1000 plants
produced.
   
    

Doesn't matter. If a kernel is fertilized by a pollen grain containing
a transgene, the new kernel will be transgenic, and will be detected as
transgenic in tests.  The kernel is either transgenic or not.  Details
about kernel structure and double fertilization are beside the point.

  
Those 5 transgenic plants  may fertilize as many  as 100 or more of
the individual cobs on plants in their immediate vicinity  or for
that mater a higher number. This spread of transgenes is independent
of selection and effects the corn crop in the generation of the
planting.
    

I think you are making this more complicated than it really is.  Every
pollen grain in the field is independent, and every silk is
independent.  The frequency of contamination depends on the gene
frequency.  It is all a numbers game.

Suppose you have 0.5% transgenic seed.  These are almost always
heterozygous for the transgene, so the gene frequency is 0.25%  The
frequency of transgenic pollen grains is about 0.25%.  The frequency of
transgenic ovules is about 0.25%.  Roughly 0.5% (.25+.25) of the
kernels borne on these plants are going to be transgenic.  Almost all
will be heterozygous.

  
The five transgenic corn plants in a thousand can and probably does
cause an unacceptable  pollution of the harvested crop.
    

As I have shown above, 0.5% contaminated seed is going to produce about
0.5% contaminated progeny.  If there is some yield drag, it will be a
little less, if there is some natural selection FOR the transgene, it
will be a little more.

  
However, the bureaucrats can fall back on the  "official" notion
that regulations of their making cannot allow endosperm to be
polluted by transgenes from
pollen. The bureaucrats and  Dale  never seem to worry about such
things as double fertilization and nature..
    

Joe, rather than go into political attack mode, simply explain how you
think the gene frequency is going to increase in the absence of
selection?

Dale

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