There are some difficulties in discussing GMOs because of the different definitions employed. At a world level the most recent, and probably the most useful, pronouncement is the so-called Cartagena Protocol on Biosafety to the 1992 Convention on Biological Diversity (SCBD, 2000).
The Protocol does not refer to genetically modified organisms but rather, for reasons that are not explicit, to living modified organisms but it is clear that the two terms should be regarded as synonymous.
In the protocol the following definitions are used:
Living modified organism means any living organism that possesses a novel combination of genetic material obtained through the use of modern biotechnology;
Living organism means any biological entity capable of transferring or replicating genetic material, including sterile organisms, viruses and viroids;
Modern biotechnology means the application of:
a. In vitro nucleic acid techniques, including recombinant deoxyribonucleic acid (DNA) and direct injection of nucleic acid into cells or organelles, or
b. Fusion of cells beyond the taxonomic family, that overcome natural physiological reproductive or recombination barriers and that are not techniques used in traditional breeding and selection;
This set of definitions is reasonably rational and scientifically defensible as it applies to transgenics but it does not specifically include nuclear transplants and nuclear cloning (not normally understood as cell fusion) and fusion beyond the taxonomic family is a somewhat arbitrary boundary not further justified.
For the purposes of this paper, we restrict our considerations to transgenic organisms although we note in passing the interesting potential in aquaculture for nuclear cloning (Zhu and Yong, 2000).
Transgenics are those organisms into which (donor) DNA has been inserted and incorporated using the in vitro techniques of genetic engineering. It is important to recognise that, as noted in the Cartagena protocol, it is the technology which defines a GMO not the source of the donor DNA and the reference frequently seen to foreign DNA is often misplaced. Thus a carp receiving and incorporating within its genome a sequence from its own DNA, is equally a transgenic, with the same fish receiving and incorporating a sequence from a daffodil. We can, however, usefully distinguish here between autotransgenic (donor and recipient of same species) and allotransgenic (donor and recipient of different species), especially as this constitutes a particularly important factor when considering aquatic species (Beardmore, 1997). However, we may note that there is some scientific opinion which seeks to redefine transgenics as referring only to the allotransgenic category referred to above (Maclean, 1998).
Figure 1. Diagram of DNA sequence of a typical construct for making transgenic organisms.