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DNA in GM Food & Feed
The government's scientific advisory committees have repeatedly tried to
reassure the public that there is nothing to fear from genetically modified (GM)
DNA, but critics disagree.
Dr. Mae-Wan Ho offers a quick guide for the perplexed
Is GM DNA different from natural DNA?
"DNA is DNA is DNA," said a proponent of
GM crops in a public debate in trying to convince
the audience that there is no difference
between genetically modified (GM) DNA and
natural DNA, "DNA is taken up by cells
because it is very nutritious!"
"GM can happen in nature," said another
proponent. "Mother Nature got there first."
So, why worry about GM contamination?
Why bother setting contamination thresholds
for food and feed? Why award patents for the
GM DNA on grounds that it is an innovation?
Why don't biotech companies accept liabilities
if there's nothing to worry about?
As for GM happening in nature, so does
death, but that doesn't justify murder.
Radioactive decay happens in nature too,
but concentrated and speeded up, it
becomes an atom bomb.
GM DNA and natural DNA are indistinguishable
according to the most mundane
chemistry, i.e., they have the same chemical
formula or atomic composition. Apart from
that, they are as different as night and day.
Natural DNA is made in living organisms;
GM DNA is made in the laboratory. Natural
DNA has the signature of the species to
which it belongs; GM DNA contains bits
copied from the DNA of a wide variety of
organisms, or simply synthesized in the laboratory.
Natural DNA has billions of years of
evolution behind it; GM DNA contains genetic
material and combinations of genetic
material that have never existed.
Furthermore, GM DNA is designed -
albeit crudely - to cross species barriers and
to jump into genomes. Design features
include changes in the genetic code and special
ends that enhance recombination, i.e.,
breaking into genomes and rejoining. GM
DNA often contains antibiotic resistance
marker genes needed in the process of making
GM organisms, but serve no useful function
in the GM organism.
The GM process clearly isn't what nature
does (see "Puncturing the GM myths", SiS
22). It bypasses reproduction, short circuits
and greatly accelerates evolution. Natural
evolution created new combinations of
genetic material at a predominantly slow and
steady pace over billions of years. There is a
natural limit, not only to the rate but also to the
scope of gene shuffling in evolution. That's
because each species comes onto the evolutionary
stage in its own space and time,
and only those species that overlap in space
and time could ever exchange genes at all in
nature. With GM, however, there's no limit
whatsoever: even DNA from organisms
buried and extinct for hundreds of thousands
of years could be dug up, copied and recombined
with DNA from organisms that exist
today.
GM greatly increases the scope and
speed of horizontal gene transfer
Horizontal gene transfer happens when foreign
genetic material jumps into genomes,
creating new combinations (recombination)
of genes, or new genomes. Horizontal gene
transfer and recombination go hand in hand.
In nature, that's how, once in a while, new
viruses and bacteria that cause disease epidemics
are generated, and how antibiotic
and drug resistance spreads to the disease
agents, making infections much more difficult
to treat.
Genetic modification is essentially horizontal
gene transfer and recombination,
speeded up enormously, and totally unlimited
in the source of genetic material recombined
to make the GM DNA that's inserted
into the genomes of plants, animals and livestock
to create genetically modified organisms
(GMOs).
By enhancing both the rate and scope of
horizontal gene transfer and recombination,
GM has also increased the chance of generating
new disease-causing viruses and bacteria.
(It is like increasing the odds of getting
the right combination of numbers to win a lottery
by betting on many different combinations
at the same time.) That's not all.
Studies on the GM process have shown that
the foreign gene inserts invariably damage
the genome, scrambling and rearranging
DNA sequences, resulting in inappropriate
gene expression that can trigger cancer.
The problem with the GM inserts is that
they could transfer again into other genomes
with all the attendant risks mentioned. There
are reasons to believe that GM inserts are
more likely to undergo horizontal transfer and
recombination than natural DNA, chief
among which is that the GM inserts (and the
GM varieties resulting from them) are structurally
unstable, and often contain recombination
hotspots (such as the borders of the
inserts).
After years of denial, some European
countries began to carry out 'event-specific'
molecular analyses of the GM inserts in commercially
approved GM varieties as required
by the new European laws for deliberate
release, novel foods and traceability and
labelling. These analyses reveal that practically
all the GM inserts have fragmented and
rearranged since characterised by the company.
This makes all the GM varieties
already commercialised illegal under the new
regime, and also invalidates any safety
assessment that has been done on them
(see "Transgenic lines proven unstable", SiS
20 and "Unstable transgenic lines illegal", SiS
21). As everyone knows, the properties of the
GM variety, and hence its identity, depend
absolutely on the precise form and position of
the GM insert(s). There is no sense in which
a GM variety is "substantially equivalent" to
non-GM varieties.
GM DNA in food & feed
In view of the strict environmental safety
assessment required for growing GM crops
in Europe, biotech companies are bypassing
that by applying to import GM produce for
food and processing only. Is GM food safe?
There are both scientific and anecdotal evidence
indicating it may not be: many species
of animals were adversely affected after
being fed different species of GM plants with
a variety of GM inserts (see "GM food safe?"
series, SiS 21), suggesting that the common
hazard may reside in the GM process itself,
or the GM DNA.
How reliably can GM DNA be detected?
DNA can readily be isolated and quantified in
bulk. But the method routinely used for
detecting small or trace amounts of GM DNA
is the polymerase chain reaction (PCR). This
copies and amplifies a specific DNA
sequence based on short 'primers strings' of
DNA that match the two ends of the
sequence to be amplified, and can therefore
bind to the ends to 'prime' the replication of
the sequence through typically 30 or more
cycles, until it can be identified after staining
with a fluorescent dye.
There are many technical difficulties
associated with PCR amplification. Because
SCIENCE IN SOCIETY 23, AUTUMN 2004