PART 2: BACKGROUND
What is genetic modification?
7. The Convention on
defines biotechnology as "any technological application that
uses biological systems, living organisms or derivatives thereof
to make or modify products or processes for specific use".
Biotechnology has been employed for millennia: fermentation, bread-making,
brewing and cheese-making were developed by the Egyptians from
about 2000 BC. A definition of
modern biotechnology, which is developing new techniques all the
time, is difficult, but current use implies the introduction of
hereditary material which could not have been achieved using traditional
The United Nations Environmental Programme guidelines for safety
define genetic modification as "modern biotechnology used
to alter genetic material of living cells or organisms in order
to make them capable of producing new substances or performing
DNA AND GENES
8. The complete set of instructions for making
any living organism, from the simplest bacteria to human beings,
is called a genome. This contains the master blueprint for all
cellular structures and activities for the lifetime of the cell
or organism. It is encoded within a set of molecules called DNA
(or RNA for some viruses).
Each DNA molecule contains many genes which are the basic physical
and functional units of heredity. Genes are "units"
of DNA coding for a single product (nearly always a protein).
There is a universal genetic code which applies from the simplest
organisms to human beings.
The code allows a stretch of DNA to specify the structure of a
particular protein. The amount of protein produced may vary depending
on cell type, timing, environmental stress and a variety of other
effects. A gene is "expressed" when the protein is synthesised.
Although most cells in the organism will contain the gene, the
degree of expression may vary from cell to cell and tissue to
tissue and thus the amount of the protein will similarly differ
9. A crop-plant genome
contains approximately 50,000 genes,
but only about 10 per cent. of the DNA is used for coding genes.
The rest includes control sequences that identify when and where
particular genes are expressed in the organism and regions whose
function is unknown.
The DNA is largely conserved during the lifetime of an organism,
but is redistributed when eggs, sperm or their equivalents are
formed. It is only in a clone that DNA is conserved unchanged
between generations. Genes, whether introduced using genetic modification
or inherently present in an organism, may be unstable, may interact
with other genes and are capable of movement within the genome.
In addition, their expression may be influenced by the environment.
10. Most organisms are only sexually compatible
within their own species, and genes cannot normally be transferred
from one species to another. Genetic modification allows the identification
of individual genes which can then be decoded, manipulated, copied
and transferred into any other organisms. In most instances the
genes are transferred along with the instructions (termed "promoters")
as to when in time and in what tissue they might be expressed.
The techniques of genetic modification allow the transfer of genes
from any organism to cells of virtually any other (using appropriate
techniques) thus removing the species barrier. Genes can thus
be transferred between bacteria, plants and animals (see paragraph
110). For plants and animals this is complicated by the need to
introduce the genes into all the cells in the organism. Although
the introduction of genes into plant cells is more difficult than
it is into animal cells, the ability to regenerate many complete
plants from a single cell makes plant biotechnology much easier.
11. The proportion of
the genome of the host organism that is modified is currently
very small: two or three genes and their associated control elements
amongst tens of thousands. The precise sequence of the genes intended
to be introduced is known. The position of insertion of the inserted
is, however, not generally known. The number of copies of the
insert introduced into the genome cannot currently be controlled
during the insertion process. There may be other genes (or partial
genes) introduced as a consequence of the technique used, but
their sequence and function is known. The introduction of copies
of the transgene may disrupt genes in the host genome. If the
disrupted genes are essential ones, the organism may not be able
to grow, and so no organism will result. If they are relatively
unimportant (such as modification of colour) the unexpected modification
may become apparent during the regeneration of the entire organism.
Disrupted genes which are involved in processes that are only
switched on during environmental stress
or which are expressed only under certain conditions in the lifetime
of the organism may not initially be identified. The disruption
may extend to changes in the timing of expression of a gene product.
These changes should however surface in the process of regenerating
the plant, or during the extensive breeding and selection processes
used to produce a commercially useful product.
METHODS OF TRANSFERRING GENES
12. There are two main
methods for the transfer of genes into plants. The first involves
the use of a soil bacterium, Agrobacterium tumifaciens,
which infects certain plants. It injects a piece of DNA into the
plant cell to attempt to take over the cell's protein manufacturing
machinery and so produce a sugar on which the bacterium can feed.
This piece of DNA is incorporated into the genome of the infected
cell. Scientists use this piece of DNA by effectively hijacking
it. Having removed some of the unneeded genes, they are able to
insert desired genes into the vacated space. Using Agrobacterium
it is possible to modify many dicotyledonous (broad leaf) plants
such as potato, rape, tobacco and tomato and the technique has
been adapted to work on maize, wheat and rice. The second method
involves the use of "biolistics" (the "gene gun")
where the desired gene package is coated around finely divided
gold particles and literally fired into plant cells. A small percentage
of the plant cells is transformed
in each case. In either method, one of the genes inserted into
the plant will produce a protein that confers tolerance to a chemical
that would normally kill the cell, a herbicide for example. When
the chemical is administered, only those cells which have been
effectively transformed and satisfactorily express the new gene
product are not killed and a complete plant may be regenerated
from these. (This
gene is termed a "marker gene" because it is used to
identify the presence of the transgene.) The laboratory modification
is only carried out on a suitable sub-set of varieties of the
crop. These varieties are then crossed (and back-crossed) using
traditional breeding technology in order to put the desired genetic
material into choice varieties for agricultural production.
These techniques are continuously being refined to make them more
efficient and predictable.
13. Other methods for inserting genes are now
under development. One method involves using a modified plant
virus to transfer the genetic material. Deleterious genes normally
found in the virus are removed and genes specifying the required
characteristics inserted. The subject plant, while growing, can
be inoculated with the modified virus and, in a few weeks, the
virus will express the desired protein in all parts of the plant.
14. The transformation of animals is much harder,
primarily because technology does not yet exist allowing the regeneration
of an animal from a single cell or group of cells. The technique
currently used for the modification of animals is the micro-injection
of DNA into embryonic cells. This provides a mosaic where only
some of the cells in the resulting organism are modified and others
are not, but it does provide a high yield of transformed animals
(described as "chimeras" as they are only partially
modified). This technique is thus not of use for the modification
of agricultural animals, but could be of considerable benefit
in medicine, for example in the treatment of cystic fibrosis.
WHAT FOODS CAN BE MODIFIED?
15. All foods are of animal, plant or micro-organism
origin and are therefore susceptible to modern biotechnology.
Many foods are the product of traditional biotechnology, which
uses micro-organisms to modify the starting material to improve
taste, texture, palatability, keeping quality or safety.
One of the earliest modern genetic modifications enabled the production
of "vegetarian cheese". The production of hard cheese
used to be dependent on small quantities of rennet, scraped from
the lining of dead calves' stomachs. The enzyme Chymosin is identical
to rennet and is produced by genetically modified yeasts or bacteria.
It was introduced in commercial cheese-making in 1991 and is now
used to manufacture 90 per cent. of hard cheeses (United Biscuits
COST OF DEVELOPMENT
16. The technology involved in genetically modifying
an organism is relatively simple and inexpensive when compared
to the costs of many other new technologies. Genetic modification
requires a broad research and knowledge base in biology, breeding,
agronomy, physiology, biochemistry and genetics. The development
process from concept to commercial crop is however exceedingly
expensive and takes many years.
11 The Convention on Biological Diversity (Rio de Janeiro,
1992) (Cm 2127) is a binding agreement signed by over 170 countries
(though not ratified by the United States). It came into force
on 29 December 1993 (DETR pp 190-1). Back
12 This would not include gene deletion or movement of genes within
the genome, as these are possible naturally (Gene deletion does
not require the deletion of an entire gene. The change or loss
of a single unit in the DNA sequence may result in the absence
of the gene product, effectively deletion.). Back
13 United Nations Environmental Programme International Technical
Guidelines for Safety in Biotechnology, 1996. These Guidelines
arose from the requirement in Chapter 16 of Agenda 21 (adopted
at the United Nations Conference on Environment and Development
in Rio de Janeiro in 1992) for the "Environmentally Sound
Management of Biotechnology" and were first developed by
the United Kingdom and the Netherlands. Back
14 Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA). Back
15 Due to this commonality, the transfer of genes from animals to
plants is thus not that remarkable (Professor Bainbridge, of the
University of Teesside and chairman of the advisory committee
on novel foods and processes, Q 682). Back
16 I.e. when the cell makes the protein. Back
17 The human genome is thought to contain between 60,000-70,000 genes
and a similar percentage of the DNA is used for coding genes. Back
18 Possibly in reserve for future use. Back
19 The inserted genes are termed "transgenes" to differentiate
them from indigenous genes. Back
20 "Secondary metabolism". Back
21 A transformed plant is a plant which has successfully been modified. Back
22 These processes are described in greater detail in the Parliamentary
Office of Science and Technology (POST) report on "Genetically
Modified Foods: benefits and risks, regulation and public acceptance",
May 1998, especially pp 3-6. Back
23 A process whereby DNA is injected directly into the cell or nucleus.
In some cases this DNA is incorporated into the genome of the
cell and is inherited by daughter cells. Back
24 For example, centuries ago, fermented drinks (like beer) arguably
became commonplace as water was not safe to drink. Contaminated
beer could be recognised far more easily than contaminated water.
25 A variety of Chymosin producing systems were permitted by ACNFP
in 1991. The first vegetarian cheese was put on sale in 1992. Back