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Glossary

ADI value

The ADI value (Acceptable Daily Intake) quantifies the daily amount of foreign matter in food that a person can ingest over a lifetime without a health risk.

The ADI value is given in milligrams per kilogram body weight and is used for e.g. food additives and pesticide residues.

ADI values are usually based on feeding experiments with rats or mice. The animals are given a diet with varying proportions of the substance under investigation. The aim is to determine the highest level at which no health effect is observed. This No Observable Effect Level (NOEL) is divided by a safety factor to give the ADI value.

The safety factor (usually 100) takes into account various incalculable factors:

  • extrapolation of the NOEL value from trial animals to humans,

  • individual differences – both between the trial animals and in humans,

  • possible unknown interactions between different additives.

Under certain circumstances, the safety factor can be increased; it can also be lower if the substance in question is a natural component of human food.

Agrobacterium tumefaciens

Soil bacterium naturally able to transfer parts of its genetic material to plant cells. It has thus been used as a tool for genetically engineering plants.

gmo-compass Agrobacteria are natural plant parasites. To create a suitable environement for themselves, they insert genes into plant hosts, which cause them to form a proliferation of cells near the soil level (crown gall). The genetic information for tumour growth is encoded on a mobile, circular DNA fragment (plasmid).

When Agrobacterium infects a plant, it transfers so-called T-DNA to a random site in the plant genome.

The natural ability of Agrobacterium tumefaciens to transfer genes is used in genetic engineering. The bacterium is used as a means of transporting foreign genes into plants (vector). To do this, the bacterial T-DNA is cut out of the bacterial plasmid and replaced with the desired foreign gene.

Transferring genes with agrobacteria is a commonly used and reliable method. It works especially well for dicotelydenous plants like potatoes, tomatoes, and tobacco. Agrobacteria are less suitable for introducing foreign genes to crops like wheat and maize.

Alleles

Alleles are the different variant forms of a gene at a particular position (locus) on a chromosome. In classic genetics different alleles are known to be responsible for variations in flower colour (for instance white/red). Each gene generally has several alleles which are characterised by having DNA sequences which differ to a greater or lesser extent.

Allergen

Substance that causes an allergic reaction.

Allergens are found almost everywhere in the environment. They occur in animal hair, pollen, insect bites, house dust mites, pharmaceuticals, and food. Currently, some 20,000 allergens have been identified.

Most allergens in food are proteins of high molecular weight and are rather resistant to gastric acid and digestive enzymes.

An allergenic food may contain several allergens; e.g. there are 15 or more different allergens in soybeans.

Allergy

An overreaction of the immune system caused by a particular substance

The symptoms of allergic reactions often vary; extreme cases can lead to life-threatening anaphylactic shock.

In most cases, allergies are caused by a protein that originates outside the body (allergen). The allergen is perceived by the body as a potentially dangerous, alien component, and an immune response is recruited. This leads to a massive release of pharmacologically active substances, predominantly histamines. Such mis-targeted immune responses are called "true" allergies, sometimes confused with pseudoallergies.

Every "true" allergy is preceded by a phase of sensitisation. First, the immune system adapts to the "alien" substance and produces antibodies. A reaction is triggered only by later contact with the allergen. The first cases of allergies to kiwi fruits did not occur until years after their introduction to the market.

A food allergy is an allergic reaction caused by food constituents or their degradation products, additives, residues, or associated microbial compounds (e.g. fungal or microbial toxins). The uptake of the particular allergen most often occurs via mucous membranes in the mouth and intestine, but can also occur through the skin or by inhalation (e.g. flour dust). Figures on the prevalence of food allergics vary; for adults it is estimated at one to five per cent, while for children under six years estimates range from three to ten percent. In Europe, the most common food allergies are to peanuts, soy, cows' milk, hens' eggs, fish, nuts, crustaceans, and celery. Food allergies are less common than other allergies such as to pollen.

Cross sensitivities can occur when an allergen can be found in more than one source. For example, people allergic to birch pollen often also have allergies to apples or nuts.

Bacillus thuringiensis (Bt)

Soil bacterium used for biological pest control - produces a crystalline protein toxic to certain types of insects.

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Bt toxin is produced by Bacillus thuringiensis in an inactive form (protoxin), which is transformed to its active form (delta-endotoxin) in the guts of certain insects. The active toxin binds to receptors in the gut, killing the insect.

Insect pests have long been fought with Bacillus thuringiensis products. Based on the premise that – as opposed to many chemical insecticides – they are harmless to humans, they are used in organic farming.

By means of genetic engineering, the genes for the active agent (Bt toxin) can be transferred from Bt bacteria to plants. There they produce the toxic agent inside the plant cells. In this way, biotechnology has been used to confer insect resistance to a number of economically important crops. Bt maize and Bt cotton are widely grown in several countries.

Bacteriophages or phages

Viruses which use bacteria as host cells

Bacteriophages consist of nucleic acid encased in a protein shell. Like other viruses, they have no metabolism of their own and specialise in certain species of bacteria. This specificity is exploited in medicine to diagnose bacterial infections (lysotypy). In (microbial) genetic engineering, bacteriophages are used as vectors to transport foreign genes to bacteria.

Bases

Building blocks of the nucleic acids DNA and RNA

Four bases are present in DNA: adenine (A), cytosine (C), guanine (G) and thymine (T). In RNA, thymine is replaced by uracil (U).

These four bases encode the genetic information; thus, the four letters A, C, G and T are sometimes called "the alphabet of life".

DNA can be visualised as a coiled ladder, the rungs of which are composed of pairs of bases; adenine always pairs with thymine, and cytosine always with guanine. A group of three bases of DNA can be recognised as a group (“codon”) specifying a particular amino acid. Hence, the sequence of codons in DNA determines the sequence of the chain of amino acids in a protein

Bioassay

A scientific experiment that assesses the effects of certain substances (toxins) on animals.

In a bioassay (biological assay), different concentrations of a test substance (e.g. Bt toxin) are administered with food. The animals chosen for testing are usually ones that are known to be, or suspected to be, sensitive to the substance. Bioassays usually measure the impact on animal growth and weight gain and frequently establish the dose at which 50% of the trial animals die (LC 50; LC = lethal concentration). The scientists check after a certain amount of time (one or more days, depending on the experimental design) how many animals have survived.

Bioassays are primarily used to test new drugs and to monitor substances that might pollute the environment.

Biolistic gun; Particle gun

A procedure used for genetic modification - genetic information is directly "shot" into plant cells

For this procedure, DNA is bound to tiny particles of gold or tungsten and subsequently "shot" into plant tissue or single plant cells under high pressure. The accelerated particles penetrate both the cell wall and membranes, slowing down as they do so. The DNA separates from the metal and can be integrated into the genetic material inside the nucleus.

This method has successfully been applied to many cultivated crops, especially monocots like wheat or maize for which a transformation with the help of Agrobacterium tumefaciens is less suitable.

A disadvantage of this procedure is the damage done to the cellular tissue.

Biopolymers

Polymers that occur in nature (macromolecules)

Biopolymers are the basic building blocks of living organisms. Examples of biopolymers are proteins, which are made up of amino acids, the nucleic acids DNA and RNA, which are made up of nucleotides, and polysaccharides such as starch and cellulose.

Biopolymers can be used to produce bioplastics. For this they are usually modified chemically using technical procedures. The basic materials usually used for bioplastics are currently starch and cellulose. Plants like maize and potatoes are increasingly being grown as renewable raw materials to supply these basic materials.

Bt protein; also Bt toxin

A protein that is toxic to chewing insects and is produced by the soil bacterium Bacillus thuringiensis and has long been used as a biological pesticide.

By means of genetic engineering, the genes for Bt toxin can be isolated from Bacillus thuringiensis and transferred to plants. The plant is thus conferred the ability to produce the insect toxin on its own.

There are different forms of Bt toxin that are specifically active against certain groups of insects. About 170 naturally occuring Bt toxins with varying specificities are known. 

For genetically engineered insect resistance, different variants of Bt genes are transferred, e.g. Cry 1Ab, Cry 1Ac and Cry 9c for maize. They differ both in terms of their length and in terms of the promoters used. The transgenic maize varieties differ depending on the Bt gene variant used, both in terms of the amount of Bt protein they produce and its distribution within the plant. Some Bt maize varieties produce the Bt protein primarily in the stem, while other produce it in all plant parts. 

Carbohydrates

A large group of organic compounds made during photosynthesis in green plants and elsewhere (also called “saccharides”).

Carbohydrates serve as energy sources, nutritional and other reserves, and structural substances. They occur in all plants and are an essential part of human nutrition. Some carbohydrates cannot be digested by humans, e.g. fibres.

All complex carbohydrates are built up from units of simple sugars (“monosaccharides”) like glucose or fructose. Carbohydrates comprising two sugar units (such as sucrose [table sugar]) are called “disaccharides”. Larger molecules such as starch are “polysaccharides”.

“Carbohydrate” is a collective term for various substances with many different chemical properties and biological functions. Their diversity results from the large variety of monosaccharides used as building blocks as well as from the ways in which they are joined to proteins and other complex molecules.

Cartagena Protocol

International agreement setting out rules on the transboundary movement of living modified organisms that are legally binding under international law.

The Protocol was adopted in Montreal in January 2000 following several rounds of negotiation. It is known as the Cartagena Protocol on Biosafety after the place at which the last round of negotiations was held. The Protocol came into force in September 2003 once it had been ratified by 50 states. 132 states have now recognised the Protocol. Those who have not signed include some countries with high levels of agricultural exports, such as the USA, Argentina, Australia and Canada.

The Protocol is a supplement to the UN Convention on Biological Diversity signed in Rio in 1992. It contains measures to protect genetic resources from the potential risks that might be posed by the release of genetically modified organisms. The negotiating partners of the Cartagena Protocol on Biosafety were the states that ratified the Convention on Biological Diversity (Conference of the Parties). 

At the heart of the Cartagena Protocol is a special information and decision-making process (Advanced Informed Agreement Procedure) to be followed in the event that living modified organisms are to be exported to another country in order to be released into the environment. The exporting nation is obliged to make available to the importing country all the information necessary for a safety assessment.

A Clearing House has been set up at international level to organise the information flow agreed in the Cartagena Protocol./p>

Chromosome

Carrier of genetic information in the cell nucleus

Chromosomes are long, thread-like structures inside the cell nucleus, consisting of DNA (the genetic information) and proteins. Before cell division, when the chromosomes are allotted to the daughter cells, the chromosomes are condensed into tightly packed units. Chromosomes can easily be stained with dye during the cell division stages, making them visible under a light microscope. This is the origin of their name, derived from the Greek words "chroma" (colour) and "soma" (body).

Every animal and plant species has a characteristic number of chromosomes. In the body cells of mammals, chromosomes always occur in pairs (diploid), with the exception of the x/y sex chromosomes in male mammals. One chromosome originates from the father, the other from the mother. They share the same form, structure and sequence of gene loci, hence the term homologous (similar) chromosomes.

However, they are not identical, since genes at the corresponding loci may exist in different forms (alleles). Organisms with more chromosomes are not necessarily more complex. Humans, for example, have 46 chromosomes, wheat 42, whilst carp have 104. A round worm gets by with only two chromosomes and the fruit fly "Drosophila melanogaster" has eight; on the other hand, "Euglena", a tiny alga, has 200 chromosomes.

Clone Library

A gene bank containing DNA sequences (clones) with accompanying information 

With the help of these banks, DNA sequences from unknown samples can be identified.

Clones

Genetically identical organisms that arise from asexual reproduction

In nature there are many examples of clones, which are named after the Greek word for 'twig' or 'branch', e.g. protozoa such as bacteria and yeasts, which reproduce through duplication. Sponges propagate by constricting off parts of the organism, also known as budding. Many types of plants, such as strawberries or potatoes, propagate through side shoots, or runners, thereby cloning themselves.

Many plants are easy to clone since they possess the natural ability to regenerate from nearly all tissues, i.e. a complete plant can be grown from, for example, a piece of leaf, and will be genetically identical to it.

The first man-made cloned animal was generated already at the beginning of the last century. However, it was not until 1996, with the birth of the cloned sheep Dolly, that cloning attracted the public eye. Until then, clones were produced from embryonal stem cells, which still possess their original ability to develop (totipotency). Dolly was the first mammal to be cloned through a special technology (nuclear transfer) from an already differentiated adult cell.

Complementary Herbicide

Herbicides used in conjunction with a specially designed, herbicide tolerant crop

If a rapeseed cultviar is genetically modified to have tolerance to an herbicide, the herbicide is considered that rapeseed cultivar's complementary herbicide.

Complementary herbicides for herbicide tolerant plants developed with genetic engineering are generally "non-selective" or "broad-spectrum" herbicides. These affect central sites of plant metabolism and are thus effective against a wide range of plants.

An herbicide tolerant crop and its respective complementary herbicide constitute an herbicide tolerance (HT) system (also known as an herbicide resistance (HR) system). In this combination, wide-spectrum herbicides like Liberty or Roundup can be applied to kill nearly all weeds without harming the crop.

Confinement

In plants: Biological measures to restrict the spreading ability of genetically modified plants

As well as genetically modified plants with modified cultivation characteristics (e.g. pest resistance), scientists are developing transgenic plants with new/modified plant substances. These plants produce substances that can be used e.g. in industrial applications or in the production of pharmaceuticals. The spreading ability of these genetically modified plants needs to be minimised. This can be achieved by e.g. suppressing reproduction (biological confinement). Using conventional breeding and genetic engineering it is possible to produce plants that

  • can no longer produce pollen

  • do not form flowers

  • or produce sterile seeds.

To restrict the spread of transgenes, researchers are also working on a genetic method that modifies the genome of the plastids. Plastids are units of a plant cell that have their own DNA. Most agricultural crop plants inherit plastid DNA maternally, i.e. not via pollen. Because of this unusual inheritance system, when plastids are genetically modified, the new gene sequences are not found in the pollen.

Corn Borer

The corn borer is the most economically important maize pest in Germany.

The first larvae of these microlepidoptera feed on maize leaves and then drill into the stem and the cob of the maize plant. In cooler, temperate climates common in Europe, the corn borer completes only one generation per year. Larvae hibernate in maize stubble, pupating in the spring.

It was was brought to North America from Europe around 1910.

There are two known strains (Z and E). In Germany the E strain is found almost exclusively in a weed: the mugwort. The Z strain is today found mainly in the maize-growing regions of southern Germany and in the Oderbruch region. The infestation limit is continually shifting towards the north-west. The first infestation was found in Lower Saxony in 2006. In Mecklenburg-Western Pomerania the little moth has already reached the Baltic coast.

There are several strategies for corn-borer control:

  • mechanical methods involve chopping up the plant remains left on the field and ploughing them under
  • Spraying chemical insecticides
  • Biological control: Trichogramma (ichneumon flies)
  • Bacillus thuringiensis (Bt) toxin, either in the form of preparations applied externally as a spray or the transgenic introduction of the Bt gene into maize plants
Cyanophycin

A storage protein produced by cyanobacteria (blue-green algae) and some other bacteria

Cyanophycin consists of polyaspartate und arginine, two non-toxic, biodegradable raw materials that have a wide variety of industrial uses. Polyaspartate can be used instead of acrylic-acid-based plastics. Until now these two amino acids have been chemically synthesised in small quantities for industrial applications.

It is thought that by introducing the gene for cyanophycin synthesis – the enzyme that produces cyanophycin – into potatoes, it will be possible to obtain polyaspartate and arginine more cheaply and on a larger scale.

 

Delayed Maturity

Breeding goal for fruits and vegetables

Many fruits like tomatoes, melons, and bananas are usually harvested before ripening. The firmness of unripe fruit facilitates mechanical harvesting and extends the period of time allowed for transport and storage.

For many fruits and vegetables, transgenic procedures have been used to develop cultivars with delayed maturity. This has been achieved by suppressing of the synthesis of polygalacturonase, an enzyme responsible for fruit softening.

Suppression of polygalacturonase production can be achieved by:

  • Inhibiting the production of ethylene (a plant hormone that triggers the ripening process) by introducing genes for enzymes that degrade ethylene precursors
  • Blocking the polygalacturonase gene using antisense technology


Transgenic tomatoes with extended shelf life were introduced to the US market: the FlavrSavr tomato was the first transgenic plant approved for commercialisation. It has since disappeared from the market. Calgene (now part of Monsanto) claimed that the limited success was due to low yields and suboptimal disease resistance. Some interpret the experience with the FlavrSavr tomato as evidence that marketing tomatoes as a specialty product is an unsuccessful strategy.

Fruits and vegetables with extended shelf lives can also be developed by conventional breeding methods.

Deletion

Removal or loss of part of a DNA sequence

Single base pairs as well as parts of a chromosome can be deleted (i.e. removed). Resulting organisms are termed “deletion mutants”.

Deletions can occur spontaneously or can be induced by various mutagens, including X-rays.

The counterpart to a deletion is an insertion.

diploid

Two sets of chromosomes

Many higher organisms have a diploid set of chromosomes during the main phase of their development, i.e. the cells contain two copies of each chromosome (one from each parent). The two sets of chromosomes are not usually identical: although they share the same form, structure and sequence of gene loci, hence the term homologous (similar) chromosomes, the genes themselves may exist in different forms (alleles).

DNA

Term used to describe the chemical make-up of the genetic information

The building blocks of DNA (deoxyribonucleic acid) are called "nucleotides", each comprising a sugar (deoxyribose), a phosphate, and a base.

These building blocks combine to form a giant molecule comprising two strands of nucleotides, the famous "double helix".

DNA is always present in the cell in conjunction with special protein molecules (histones), which act as "spools" around which the DNA strands wind.

The sequence of nucleotides in each of the two strands carries the entire genetic code, which is therefore present in full in every cell of an organism. 

The two strands are held together by the pairing of the bases adenine (A), cytosine (C), guanine (G) and thymine (T). A always pairs up with T and C with G. This complementary structure enables DNA to replicate itself during cell division. It divides like a zip into two single strands, each of which then replicates to form a double strand again. DNA also splits open to reveal sites which are "read" by RNA during the transfer of genetic information. A gene is a specific sequence of DNA.

In 1953 James Watson and Francis Crick unlocked the molecular structure of DNA.

It was previously thought that each gene provided the blueprint for a specific protein (one gene, one protein hypothesis), but we now know that a specific gene can code for different proteins with the aid of complex regulatory mechanisms. Protein-coding genes, however, account for only 1 to 2% of DNA. In humans this amounts to around 30,000 to 40,000 genes, which code for an estimated 300,000 proteins. Around 95% of DNA is comprised partly of regulatory units, but mainly of sequence segments whose functions have yet to be discovered.

DNA methylation

  A natural regulatory process in the cell, which controls gene activity

Special enzymes known as methyltransferases transfer a methyl group (CH3 group) to the DNA building block cytosine at specific sites in the genome to produce methylcytosine. When this process affects regulatory DNA segments, it modifies the ‘readability’ of a gene. The conversion of cytosine is reversible.

The methylation of DNA bases has various biological functions. In bacteria, methylation is used to mark the bacteria's own DNA (to distinguish it from foreign DNA) and is involved in error correction in DNA synthesis.

In higher organisms, methylation is used to mark active and inactive regions of DNA.

Since DNA methylation affects the transcription of genetic information without changing the DNA sequence itself, it is one of the principal mechanisms of epigenetics.

DNA microarray

DNA chip that provides information about the activity of individual genes

DNA microarrays help identify possible changes in the activity (expression) of certain genes as a function of various factors. In genetic engineering, the method is used among other things to compare expression in transgenic and non-transgenic plants.

  • In a first step the mRNA (messenger RNA) of the organism under investigation is isolated. The quantity and composition of the mRNA in a cell provide an indication of which genes are expressed with what frequency. The mRNA can be used to reconstruct the DNA fragments that contain the information expressed by the mRNA. This reconstructed DNA (cDNA) is marked using a fluorescent dye.
  • The DNA microarray contains all the genes of the organism under investigation on a glass plate, the ‘gene chip’, as an arrangement (or array) of single-stranded DNA. The generated cDNA is inserted onto the DNA chip and the cDNA sequences bind (hybridise) to their complementary counterpart on the array. 
Dormancy

In plants: seed dormancy

Dormancy, also called primary dormancy, in seeds is a state during which no germination takes place, even if the environmental conditions are favourable for germination. The presence of a certain level of primary dormancy is an important trait in modern oilseed rape varieties. It prevents premature germination of ripe seeds inside the pods before harvesting. By contrast, sown rape seeds usually germinate without delay.

However, unfavourable environmental conditions can interrupt the germination process, triggering secondary dormancy, e.g. if rape seeds in the soil are exposed to drought stress in the absence of light.


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