Since the early 1980s developments in genetic engineering have made it possible to produce genetically modified organisms. A gene from one organism is isolated and transferred to cells of another organism, where it is incorporated into the recipient’s chromosomes and expressed. Such transgenic organisms can exhibit quite novel characteristics. Commercial applications of this new technology have ranged from the production of human hormones in bacteria and vaccines in yeasts to the development of genetically modified (GM) crop plants. More recently, the techniques of genome editing offer the potential to make specific targeted mutations that will enhance or suppress expression of certain genes or to introduce DNA sequences that will confer new traits, such as disease resistance.

Techniques

Much of the work with genetic modification of plants involves protoplasts, cultured spherical cells from which the cell walls have been removed. The Ti plasmid (see illustration) of Agrobacterium tumefaciens, the bacterium that is responsible for the tumorous growths of crown-gall disease in plants, has been used successfully as a vector with certain dicotyledons, including tobacco, tomato, potato, soyabean, and cotton. It works much less well with grasses, cereals, and other monocots. In these plants various other techniques are available, including:

• • electroporation—treatment of cells by exposure to an electric field that renders them transiently permeable to DNA fragments;

• • microinjection—injection of DNA directly into the cell nucleus;

• • biolistics—‘shooting’ a cell with a DNA-coated tungsten microprojectile, which penetrates the cell wall with minimal damage.

To produce a transgenic animal the novel genes are inserted at a very early stage of development, e.g. the early embryo or the pronucleus of a fertilized egg, typically using microinjection. The recombinant embryos are then transferred to the uterus of a foster mother where they complete their development.

Applications

Plants

• • tolerance to herbicides

• • improved insect resistance or drought tolerance

• • production of materials (e.g. plastics) or drugs

• • longer ‘shelf life’; improved nutritional qualities (e.g. β‎-carotene in golden rice)

Animals

• • production of therapeutic proteins in milk (e.g. human growth hormone)

• • potential for improved growth rates and milk yields

• • potential for production of organs for human transplants

Risks

The use of GM organisms in the environment poses certain potential problems. For example, genes for herbicide or insect resistance may spread from crop plants to wild plants, with possible serious consequences for both agriculture and natural ecosystems. Farmers may be faced with new ‘superweeds’, while insect populations could decline. Moreover, the products of GM crops have to be fully evaluated to ensure that they are safe to eat. Genetic modification of animals often has unforeseen side-effects and raises ethical issues about such treatments.