The Genetics Controversy - Agri-culture: Reconnecting People, Land and Nature - page 127

to benefit. Like all new ideas, though, it requires balance and case-by-case
analysis because we do not yet know all of the risks and benefits.
So, what is biotechnology? It involves making molecular changes to
living or almost living things. It has a long history, dating back 4000 years
to the invention of fermentation, bread-making, brewing and cheese-
making by Egyptians and Sumerians, grafting techniques developed by
the Greeks, and many years of selective breeding by farmers. Modern
biotechnology and genetic modification are, by contrast, the terms given
to the transfer of DNA from one organism to another, thereby allowing
the recipient to express traits or characteristics normally associated just
with the donor. 1 As these transfers or mixes do not occur in nature, the
scope for genetic modification is greater than in conventional animal or
plant breeding, even though advanced breeding already involves types of
genetic manipulation, including clonal propagation, embryo transfer,
embryo rescue and mutant selection.
The process of genetic modification involves, firstly, identifying and
isolating the novel gene, called the transgene , as a section of DNA. This
transgene codes for the production of a protein, usually an enzyme, that
catalyses a novel biochemical reaction or pathway in the host plant or
animal. This is then linked to a suitable promoter - another DNA sequence
that regulates the expression of the gene. This construct of transgene plus
promoter has to be introduced into the target organism's own chromo-
some. Two methods are currently available: the use of the bacterium
Agrobacterium and the gene gun. Agrobacterium naturally transfers DNA to
its host plant, causing diseases or the formation of galls. But for the
purposes of genetic modification, its plant-gall inducing capability has
been removed, and it works as a vector to transfer DNA. Initially, this
method only worked for broadleaf plants, but has now been developed
for transforming cereals. The gene gun, by contrast, fires microparticles
of gold or tungsten coated with the transgene constructs into the target
cells.
Neither process, though, is predictable since incorporation of the
transgenes into the host DNA is largely random. Location in the genome
is vital, as only some of the individual organisms will express the desired
characteristics. Once these have been identified, they are grown and bred
conventionally. This process of identification requires the use of a selective
marker - some way to distinguish at cellular level the cells that contain
the transgene and those that do not. The construct thus contains a third
element - a marker gene. The easiest markers confer resistance to anti-
biotics or herbicides, so that non-genetically modified cells can easily be
filtered out. However, antibiotic markers are a cause for concern, given
their overuse in farming and medicine, combined with the growth of