> Dale, are you telling us that the % sensitivity of the PCR
> changes from whole grain to flour?
> Is this due to the distribution of dna fragments between the
> various parts of the grain, with relatively more in the flour
> than in the whole seed?
No, and no. Discrete seeds are either GMO or not. Assuming infinite
sensitivity of the PCR itself (not really true, but not too far off), net
assay sensitivity is purely a function of how many seeds are bulked, ground
and mixed to make the working sample. This is because the probability of
finding one or more GMO seeds in your sample is a function of sample size
and true frequency of seeds in the lot. I can send you SAS code to
calculate this if you want.
On the other hand, if the whole lot is ground into infinitely small pieces
(again, not a completely accurate assumption), even one GMO seed in a huge
batch of grain would make the whole thing positive. Of course, this isn't
quite true because PCR is not infinitely sensitive, flour particles are of
finite size, and the "batch" is rarely well mixed. But things are expected
to become a whole lot less predictable, and more sensitive in practice once
the grain is ground.
At the agronomy meetings last week I heard of a load of wheat ground into
flour in Taiwan, which ended up testing positive for GMO. This was mighty
peculiar, since there are no GMO wheat varieties on the market. Probably, a
few grains of GMO corn were mixed in with the wheat.
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