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 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.
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 __________________________________ 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 <firstname.lastname@example.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 mailto:email@example.com 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