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Re: Stupid Question re Genetics
Hi Dale and Chuck,
Getting back to Wytze's original concern , paraphrased, will a corn crop
planted at an acceptable limit, say 5 transgene polluted seeds per
thousand produce a crop of corn with 0.5% transgene pollution in the
food. The answer is; the first crop would produce 5 transgenic plants
per thousand but the corn crop could have more than 50 cobs per
thousand containing transgenic grains depending on wind conditions,
placement, etc. When the food was recovered the actual percentage
transgene production in food would depend on endosperm production
mainly in the polluted cobs. The percentage contamination of food would
be on a mass basis not a grain per grain basis. It seems likely that
food contamination with as much as 5% to 10% transgenes could be recovered.
Any way you figure it setting transgene pollution on a basis of .5%
of grains is not a predictable way to regulate transgenes in food. If
the regulation was set as transgenes making up .5% of the mass of the
planted seeds then you would still be stuck with uncertainty depending
on the proportion of endosperm to embryo in the seeds.
For those kinds of reasons it is most reasonable to set transgene
contamination as the lowest detectable level, that may as few as 1
grain in a million or less.
Sincerely, Joe
Dale Wilson wrote:
Hello Chuck,
"In corn, the embryo (including the scutellum) is very large, making
up a substantial fraction of the kernel. In any case, if the
(conventional) 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."
I added the word (conventional) for clarity. Would not the
frequency of the kernel that is a hybrid between a conventional and a
transgenic plant be transgenic 50% of the time?
In the way I phrased the senario (a transgenic pollen grain on a
conventional ovule) the kernel would always be transgenic. It would be
heterozy...er- hemizygous. At the locus where the transgene had been
inserted, one chromosome (from the pollen) would have the transgene,
while the homologous chromosome (from the mother plant) would not. The
transgene is dominant, and the cells in the embryo and probably the
endosperm would express the trait (depending on the promoter I guess).
Now, if I took a typical transgenic hybrid or incidental transgenic
contaminant plant (generally hemizygous) and put a tassel bag on it and
used the bulk pollen to pollinate the silks of a conventional corn
plant, half the kernels would be transgenic. Why? Because the pollen
shed on the transgenic plant is 50% transgenic (the plant is
hemizygous).
Now, suppose I got a Bt male parent inbred and put a tassel bag on one
of THOSE and pollinated a conventional ear with the bulk pollen. 100%
of the resulting kernels would be transgenic. Why? because the
pure-line seed of the inbred is homozygous, and 100% of the pollen
grains from these plants are transgenic.
I know I am missing
something. Please help out.
Maybe you are over-complicating this in your mind, or getting
distracted by list-chatter.
Dale
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