GMO Myths and Truths

and function of the protein for which it is the
blueprint.
● The GM gene can be inserted into a region of
the plant’s DNA that controls the expression
of one or more genes of the host plant,
unnaturally reducing or increasing the function
of those genes.
● Even if the GM gene is not directly inserted
into a host gene or its control region, its mere
presence within an active host gene region can
alter the ability of that region of the plant’s
DNA to form chromatin (the combination of
DNA and proteins that make up the contents
of a cell nucleus) structures that influence
the ability of any gene in that region to be
expressed. The inserted gene can also compete
with host genes for gene expression control
elements (comparable to switches that turn the
expression of a gene on or off) or regulatory
proteins, resulting in marked disturbances in
the level and pattern of gene expression.
Since the insertion of the GM gene is an imprecise
and uncontrolled process, there is no way of
predicting or controlling which of the plant’s genes
will be influenced – or the extent of the changes
caused by the inserted gene.
Genome-wide mutations
In most cases, the insertion process is not clean.
In addition to the intended insertion, fragments
of the GM gene’s DNA can be inserted at other
locations in the genome of the host plant. Each of
these unintended insertional events may also be
mutagenic and can disrupt or destroy the function
of other genes in the same ways as the full GM gene.
It is estimated that there is a 53–66%
probability that any insertional event will disrupt
a gene. 1 Therefore, if the genetic modification
process results in one primary insertion and two
or three unintended insertions, it is likely that at
least two of the plant’s genes will be disrupted.
Research evidence also indicates that the
GM transformation process can also trigger
other kinds of mutations – rearrangements and
deletions of the plant’s DNA, especially at the site
of insertion of the GM gene 1 – which are likely to
compromise the functioning of genes important to
the plant.
Mutations caused by tissue culture
Three of the central steps in the genetic
modification process take place while the host
plant cells are being grown in a process called cell
culture or tissue culture. These steps include:
(i) The initial insertion of the GM gene(s) into
the host plant cells
(ii) The selection of plant cells into which the GM
gene(s) have been successfully inserted
(iii) The use of plant hormones to induce cells
selected in (ii), above, to develop into
plantlets with roots and leaves.
The process of tissue culture is itself highly
mutagenic, causing hundreds or even thousands
of mutations throughout the host cell DNA. 1,2
Since tissue culture is obligatory to all three steps
described above and these steps are central to the
genetic engineering process, there is abundant
opportunity for tissue culture to induce mutations
in the plant cells.
Given the fact that hundreds of genes may
be mutated during tissue culture, there is a
significant risk that a gene important to some
property such as disease- or pest-resistance could
be damaged. In another example, a gene that plays
a role in controlling chemical reactions in the plant
could be damaged, making the crop allergenic or
reducing its nutritional value. The effects of many
such mutations will not be obvious when the
new GM plant is growing in a greenhouse and so
genetic engineers will not be able to select them
out.
In the process of insertion of a GM gene into
the plant host DNA (step i, above), the GM gene
is linked with an antibiotic resistance “marker”
gene, which will later enable the genetic engineer
to identify which plant cells have successfully
incorporated the GM gene into their genome.
The host plant cells are then exposed
simultaneously to the GM gene and the antibiotic
resistance gene in the hope that some will
successfully incorporate the GM gene into their
genome.
This is a very inefficient process because
genomes are designed to exclude foreign genetic
material – for example, invading viruses. So out
of hundreds of thousands or even millions of host
plant cells exposed to the GM gene, only a few will
GMO Myths and Truths 14