Genetic modification

Selecting for variability within existing populations arising from genetic recombinations resulting from sexual reproduction. It is noteworthy that most modern crops have been so altered using this technique that it is difficult to identify their wild progenitors. Variability in dog breeds provides another example of the results of this type of GM.

Crossing closely related species. For example, modern bread wheat has arisen from two sequential crossings of, in total, three species.

Isolating mutants. For example, herbicide resistant oilseed rape has been developed from plants that appeared spontaneously in Canadian fields.

The identification and isolation of a linear polymer of nucleotides that will either direct the synthesis of a protein with desired characteristics (a gene: see Genetics §2), or alter the level of protein synthesis directed by another gene. The process of isolation of specific nucleotide sequences requires in particular the action of bacterial enzymes that cut nucleotide polymers in precise locations identified by their nucleotide sequence. These are called restriction enzymes, the first of which was isolated in 1970. (More recently, another technique for the rapid in vitro replication of DNA sequences, termed the polymerase chain reaction or PCR, has become an increasingly central tool to aid the isolation of desired DNA fragments.)

The movement of the desired gene(s) into another organism. Genes are usually moved into other organisms by exploiting natural pathogens whose mode of infection involves the injection into the host of genetic material. Herbert Boyer and Stanley Cohen performed the first successful gene transfer in 1973.

This gene transfer occurs into a single cell. When genetically modifying plants or animals, an entire organism must then be regenerated from this single cell. Thus, transfer into single-celled embryos is technically desirable, as these are programmed for growth into a multicellular organism. Plants, however, have the useful trait of totipotency, whereby cells from the adult plant have the ability to regenerate into new adults – thus a range of cell types can be used for gene manipulations. The recent cloning of mammals from adult cells, most famously ’ Dolly’ the sheep, opens the door for this technology being transferred to mammals.