Hi Chuck,
Friends, the ongoing dialogue over GM crop genetics is
getting into very interesting deep water.
I just got back from a little vacation on Kelly's Island. Looks like I
missed some interesting debate. But I will catch up as time allows.
"Transgenic crops are either homozygous or hemizygous but practically
never heterozygous. A heterozygous transgene would normally arise if
a
homozygous diploid suffered a mutational change on one of the alleles
to inactivate the allele or to alter its activity."
Some people use the term hemizygous when there is not a corresponding
allel on the homologous chromosome. I think this is needless
hair-splitting. My point was that most transgenic corn varieties only
have the transgene on one of the homologous chromosomes. The transgene
is only placed in one of the parents used in hybrid seed production,
usually the male parent. This is done because it is cheaper and more
flexible. Thus, when typical transgenic corn produces gametes, half
bear the transgene and half do not.
First, if Monsanto had a RR soybean variety that was
heterozygous, it would deep six it because it would not perform with
sufficient reliability, right?
The situation is entirely different with soybeans because they are a
self-pollinating species. They are essentially homozygous at all loci.
They must be so to be stable and to breed true. But hybrid corn does
not breed true, whether it is transgenic or not. It is not a pure
line, it is a hybrid.
when the pollen from a
homozygote RR variety crosses with a non-GMO variety. The seed
produced by
that conventional-non-GMO plant pollinated cross could be
heterozygous --
or if I understand Joe, hemizygous -- but never homozygous, or
perhaps I
just drowned.
Don't drown in the jargon. In this context, heterozygous and
hemizygous have the same practical consequence. That is that the
frequency of the transgene is one-half the frequency of the frequency
of transgenic individuals.
The only reason this is important is to allow accurate estimation of
the frequency of transgenic contamination in OP populations of
cross-pollinated species. The situation is more complicated for
stacked products (more than one transgene). But in all these cases,
the methods to calculate the probability of encountering any particular
combination have long been worked out based on gene frequencies.
Dale
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