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further comment on heterozygous



Dale Wilson commented about transgenes as follows  "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."
Can transgenic constructions be heterozygous? The term heterozygous applies to alleles at a locus on homologous chromosomes. Heterozygous implies that a transgene such as a Bt cry gene or a bacterial gene in roundup ready crops has a natural allele at the locus into which the transgene was inserted. Crops with two identical transgenes at a locus are homozygous and transgenic crops are often homozygous. In the case of the single transgene copy there is no homologous allele at the locus of the transgene and such crops , as in transgenic corn, are hemizygous (a gene at a locus that lacks a homologous allele at the locus). 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.
Dale is the only "expert" I have encountered who calls the single transgene with no allele at the locus of the transgene heterozygous. However, the corporate culture has a way of using words! Hope others will think about what we say about homozygous, heterozygous and hemizygous, Dale uses the term to make transgenes more natural than they are!
Sincerely, Joe

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