How do breeders determine which
plants express the trait encoded by the transgene?
One option is for the breeders to observe the
plant for the trait of interest. However, if
the trait is not easily detectable in the field
(such as seed protein) then this method is inefficient.
Another option is to utilize the selectable
marker that was inserted during transformation.
However, this is not feasible if the selectable
marker gene was an antibiotic resistance gene.
Also, the selectable marker gene sometimes inserts
into a different chromosome than the transgene.
As a result, some offspring will have the transgene
and not the selectable marker gene and vice
Plant breeders often use an ELISA test, which
detects the presence of the protein encoded
by the transgene in a sample of plant tissue.
This test can be quickly done in the field using
a kit and a small sample of tissue and will
give a simple positive or negative response.
Sometimes a more sophisticated test called
PCR is used. The second method tests for the
presence of the transgene itself. This laboratory
method, called PCR (Polymerase Chain Reaction),
is much more time consuming and expensive. However,
it can be used to detect the presence of a transgene
in tissues that are not expressing the gene.
A final option sometimes used by major companies
is genetic fingerprinting. This technique can
be used to not only identify the presence of
the transgene, but find which plants, through
the natural variation in breeding, have obtained
a greater percentage of the elite inbred genes.
This can potentially shorten the number of generations
required for backcrossing. Athough very advantageous,
this technique is also very time consuming and
expensive, and could not be performed on a large
number of lines.
All of these detection methods are important
tools that help the plant breeder identify the
plants they should be making crosses with.
It takes the breeder at least two or three
years to derive a backcross line that is the
genetic equivalent of the elite line plus the
event. After that point the plant breeder can
work with the genetically engineered line in
the same manner they work with other parents
in their breeding program. Many companies have
taken advantage of genetic fingerprinting technology
and year-round nurseries to maximize the efficiency
and speed of backcross line development.