2.2.1 Do GM crops pose unique problems?
It is perhaps overly simplistic to take the line that only 'natural foods' should be commended and that GM plants are unnatural. Arguably, very few of our modern foodstuffs can be termed 'natural', in that they are not derived from naturally evolved crops. Tremendous changes in genetic make-up have been achieved by conventional (i.e. non-GM) breeding methods. Traditional plant breeding involves selection of individuals seen as superior, and then crossing, i.e. transferring the pollen of one superior plant to the female parts of another superior plant of the same species. Whilst those suspicious of GM crops do not argue against this form of production of new crops, it is hard to argue that it is in any way 'natural'. More complex technological procedures falling under the category of conventional plant breeding include:
Intergeneric and interspecific crossing between distinct plant genera and species, are commonly brought about artificially, to produce what could be called 'man-made' crops. One example is Triticale (Figure 1a), which is a hybrid between wheat (Triticum spp.) and rye (Secale spp.), used in animal feeds and (without any level of public concern) in the manufacture of multigrain bread for human consumption.
Haploid breeding (also known as doubled-haploid breeding) involves the treatment of normal (diploid) plants so as to produce haploid offspring, which have only one chromosome from each pair in the nuclei of their cells. The haploid plants are treated with a chemical that induces each single chromosome to double, producing an exactly identical copy. This means that the plant is homozygous for all traits. The method produces true-breeding crops more quickly than traditional plant breeding, and commercial varieties of barley have been produced in this way.
Mutation breeding involves exposing crop plants to appropriate doses of ionising radiation, or another mutagenic agent . This raises the rate of mutation, and may 'knock out' one or more genes. Almost all of the resulting mutations are deleterious, and lead to unhealthy and/or infertile plants. Occasionally, a previously unknown feature arises that may be beneficial, and this can be exploited and a new strain developed. It has been estimated that more than 1400 'improved' crop varieties (technically termed cultivars), in a wide range of species (e.g. see Figure 1b), have been developed through mutation breeding in the past 50 years, with no evidence of public concern.
These few examples testify to the fact that a form of 'genetic technology' has been part of common agricultural practice for many years. However, these techniques came into widespread use at a time when there appeared to be less public interest in agricultural technology. You might speculate that the introduction of such techniques might inspire a great deal more public concern today.
What is distinctive about GM as opposed to these more orthodox methods of plant breeding?
It can bring about the selective and specific transfer of one or more genes from radically different organisms.
With more conventional plant breeding, crossing generally requires the combination of two entire genomes, which means that in addition to what may be the single gene of interest, others are brought along in the process. Take a conventional wheat-breeding programme, where the intention is to introduce a foreign gene from a distantly related cultivar into an existing commercial cultivar. By conventional crossing, not only would the new useful gene be introduced, but also a whole range of other genes, much less likely to be advantageous to the newly developed cultivar. It may be that these inadvertently introduced genes produce a readily identifiable feature - perhaps many such plants are tall, in which case the plant breeder can easily identify and eliminate them. More typically, such additional genes are far less easy to eradicate.
Critics of GM claim that the process involves genetic transformation of a type and degree that is unique. They emphasise factors such as the extensive breaking and joining of the DNA of the host genome and what some call 'illegitimate recombination' and 'scrambling' of both foreign and host DNA at the points where transgenes become inserted. By this logic, GM technologies are imprecise and inefficient. It is claimed that the removal of genes from their normal context and randomly inserting them in a totally new genetic environment could lead to 'position effects', resulting in variable levels of transgene expression as well as disruption of host gene function. Critics of GM claim that many of the enthusiastic proponents for GM are following the traditions of genetic determinism and adopting simplistic 'reductionist' modes of thought about the science of genetics. By that 'reductionist' logic, organisms are no more than collections of genes, with each gene acting in isolation. Campaigning organisations such as Gene Watch and Greenpeace have contrasted GM techniques with traditional breeding:
Natural sexual reproduction methods used in plant breeding preserve the complex gene organisation and regulatory networks that have evolved over vast periods of time.
You may know of concepts in genetics such as 'position effects', 'functional integrity' and 'natural sexual reproduction methods'. These are very relevant to this discussion. If you know of such terms you may well know something of the complexity and subtlety of plant and animal genomes, of the interactions between genes and the ease with which control mechanisms can be upset. The concern about 'position effects' in the context of GM is genuine, although transgenic crops described in S250_1 Gene manipulation in plants have, as yet, shown no obvious deleterious effects. It is likely that most deleterious effects of genetic modification, like those of conventional breeding, result in unhealthy or infertile plants, unlikely to develop further. When critics of GM commend 'natural sexual reproduction methods' the pro-GM lobby often sees this as problematic, pointing out that natural processes are themselves often error-strewn and may give rise to unexpected outcomes.