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Biotechnology Glossary A-I


Active ingredient The individual element of a given compound or mixture responsible for that compound’s primary characteristics.

Active site (Specific to enzymes) The area on the surface of an enzyme where a molecule binds to increase the chemical rate of a reaction. Also see Enzyme.

Acute Respiratory Distress Syndrome (ARDS) A malfunction of the lung resulting from injury to the small air sacs and the capillaries of the lungs. Upon injury, blood and fluid leak into the air sacs, making breathing difficult. The condition can be fatal.

Agrobacterium tumefaciens A bacterium that causes crown gall disease in some plants. The bacterium characteristically infects a wound, and incorporates a segment of Ti plasmid DNA into the host genome. This DNA causes the host cell to grow into a tumour-like structure that synthesizes specific opines that only the pathogen can metabolize. This DNA-transfer mechanism is exploited in the genetic engineering of plants.

Agrobacterium tumefaciens-mediated transformation The process of DNA transfer from Agrobacterium tumefaciens to plants, that occurs naturally during crown gall disease, and can be used as a method of transformation.

Agronomic(s) The science of soil management and crop production.

Albumin A human protein that makes up part of blood plasma. It helps to regulate the pressure and volume of plasma in the body. It is also responsible for transporting fatty acids in blood. Also see Protein and Fatty Acids.

Allergen An antigen that provokes an immune response.

Allergenicity Refers to the potential of a substance to cause allergies.

Amino acid A compound containing both amino (-NH2) and carboxyl (-COOH) groups. In particular, any of 20 basic building blocks of proteins having the formula NH2-CR-COOH, where R is different for each specific amino acid.

Ammonia A colourless gas made up of one nitrogen and three hydrogen atoms. It is highly alkaline in water based solutions.

Amniocentesis A procedure for obtaining foetal cells for prenatal diagnosis by sampling theamniotic fluid from a pregnant mammal. Cells are cultured, and the karyotype is checked for known irregularities (e.g. Down’s syndrome and spina bifida in humans).

Angelman’s Syndrome A genetic disorder caused by abnormal function of the gene UBE3A. It causes developmental problems, speech impairment and seizures.

Anovulation Lack of ovulation caused by a medical condition, drug, or menopause.

Anti-infective Describes agents that fight infections.

Antioxidant Compounds that slow the rate of oxidation reactions.

Antisense RNA An RNA sequence that is complementary to all or part of a functional mRNA molecule, to which it binds, blocking its translation.

Antibiotic A class of natural and synthetic compounds that inhibit the growth of, or kill some micro-organisms. Antibiotics are widely used medicinally to control bacterial pathogens, butresistance in bacteria to particular antibiotics is often rapidly acquired through mutation.

Antibiotic resistance The ability of a micro-organism to disable an antibiotic or prevent its transport into the cell.

Antibody (Abbreviation: Ab). An immunological protein produced by the lymphocytes in response to contact with an antigen. Each antibody recognizes just one antigenic determinant of one antigen and acts by specifically binding to it, thus rendering it harmless. Those from the IgG antibody class are found in the bloodstream and used in immunoassay.

Antibody binding site The part of an antibody that binds to the antigenic determinant.

Antigen A macromolecule (usually a protein foreign to the organism), which elicits an immune response on first exposure to the immune system by stimulating the production of antibodies specific to its various antigenic determinants. During subsequent exposures, the antigen is bound and inactivated by these antibodies.

Antigenic determinant The individual surface feature of an antigen, that elicits the production of a specific antibody in the course of the immune response. Each antigenic determinant, typically a few amino acids in size, causes the synthesis of a different antibody and thus exposure to a single antigen may result in the expression of a number of antibodies.

Apoptosis The process of programmed cell death, which occurs naturally as a part of normal development, maintenance and renewal of tissue. Differs from necrosis, in which cell death is caused by external factors (stress or toxin).

Aquaculture Farming of aquatic organisms, including fish, molluscs, crustaceans and aquatic plants.

Arthropods The largest animal kingdom, branch. It includes insects, arachnids and crustaceans. This group can be identified by their segmented bodies, and paired, jointed antennae, wings or legs.

Assay 1. To test or evaluate. 2. The procedure for measuring the quantity of a given substance in a sample (chemically or by other means).

Assisted hatching Sometimes used during in vitro fertilization, this procedure removes the outer coating of the mother’s egg so it can implant properly in the uterus. Also see in vitro fertilization.

Autoantibodies (In autoimmune diseases) Antibodies made against the body’s own tissue. Also see Antibody.

Auto-immunity A disorder in the body’s defence mechanism in which an immune response is elicited against its own (self) tissues.

Auto-immune disease Disorder in which the immune systems of affected individuals produce antibodies against molecules that are normally produced by those individuals (called self antigens).

Autoradiograph A technique for visualizing the presence, location and intensity of radioactivity in histological preparations, paper chromatograms or electrophoretic gel separations, obtained by overlaying the surface with X-ray film and allowing the radiation to form an image on the film.

Auxotroph A mutant cell or micro-organism lacking one metabolic pathway present in the parental strain, and that consequently will not multiply on a minimal medium, but requires for growth the addition of a specific compound, such as an amino acid or a vitamin.


B cell An important class of lymphocytes that mature in bone marrow (in mammals) and the Bursa of Fabricius (in birds) and produce antibodies. Largely responsible for the antibody-mediated or humoral immune response, giving rise to the antibody-producing plasma cells and some other cells of the immune system.

B lymphocyte See: B cell.

Bacillus A rod-shaped bacterium.

Bacillus thuringiensis (Abbreviation: Bt). A bacterium that produces a toxin against certain insects, particularly Coloeoptera and Lepidoptera; a major means of insecticide for organic farming. Some of the toxin genes are important for transgenic approaches to crop protection.

Backcross Crossing an individual with one of its parents or with the genetically equivalent organism. The offspring of such a cross are referred to as the backcross generation or backcross progeny.

Bacteriophage (Abbreviation: phage). A virus that infects bacteria. Altered forms are used as cloning vectors.

Bacterium (pl.: bacteria) nicellular prokaryotic organisms, without a distinct nucleus. Major distinctive groups are defined by Gram staining. Also classified on the basis of oxygen requirement (aerobic vs anaerobic) and shape (spherical = coccus; rodlike = bacillus; spiral = spirillum; comma-shaped = vibrio; corkscrew-shaped = spirochaete; filamentous).

Balloon angioplasty A surgical procedure for re-opening a clogged artery. A balloon is attached to a tube and inserted into a blocked or narrowed artery. When it reaches the site of the blockage it is inflated to re-open the passage way.

Base One of the components of nucleosides, nucleotides and nucleic acids. Four different bases are found in naturally occurring DNA – the purines A (adenine) and G (guanine); and the pyrimidines C (cytosine) and T (thymine, the common name for 5-methyluracil). In RNA, T is replaced by U (uracil).

Base pair The two separate strands of a nucleic acid double helix are held together by specific hydrogen bonding between a purine and a pyrimidine, one from each strand. The base A pairs with T in DNA (with U in RNA); while G pairs with C in both DNA and RNA. The length of a nucleic acid molecule is often given in terms of the number of base pairs it contains.

Beta cells Insulin-producing cells in the pancreas. If these cells are destroyed, Type I diabetes develops. Also known as islet cells.

Biochemical pathway A series of biological reactions leading up to the creation of a particular product or event.

Biochemistry The study of the chemistry of living organisms, especially focussing on metabolism.

Biodiversity The variability among living organisms from all sources, including, inter alia, terrestrial, marine and other ecosystems and the ecological complexes of which they are part; this includes diversity withinspecies, between species and of ecosystems.

Bio-engineering The use of artificial tissues, organs and organ components to replace parts of the body that are damaged, lost or malfunctioning.

Bio-informatics The use and organization of information of biological interest. In particular, concerned with organizing bio-molecular databases (particularly DNA sequences), utilizing computers for analysing this information, and integrating information from disparate biological sources.

Biological response modifiers Proteins that modify or enhance an immune or other biological response.

Biologically active Describes a specific substance which has an effect on the metabolic activity of living cells. Also see Metabolism.

Bioluminescence The enzyme-catalyzed production of light by a number of diverse organisms (e.g. fireflies and many deep ocean marine organisms). Utilized as a reporter gene in plant transgenesis, and for the detection of food-borne pathogenic bacteria.

Biomass 1. The cell mass produced by a population of living organisms. 2. The organic matter that can be used either as a source of energy or for its chemical components. 3. All the organic matter that derives from the photosynthetic conversion of solar energy.

Biomass proteins The total weight of all protein, in a given area, organism or group of organisms.

Biome A major ecological community or complex of communities, extending over a large geographical area and characterized by a dominant type of vegetation.

Biomolecules Any molecule that is involved in the maintenance and metabolic processes of living organisms. Biomolecules include carbohydrate, lipid, protein, water and nucleic acid. Also see Metabolism, Protein and Nucleic Acids

Bioprocess Any process that uses complete living cells or their components (e.g. enzymes, chloroplasts) to effect desired physical or chemical changes.

Bioreactor A tank in which cells, cell extracts or enzymes carry out a biological reaction. Often refers to a fermentation vessel for cells or micro-organisms.

Biosynthesis Synthesis of compounds by living cells, which is the essential feature of anabolism.

Biotechnology 1. “Any technological application that uses biological systems, living organisms, or derivatives thereof, to make or modify products or processes for specific use” (Convention on Biological Diversity). 2. ” Interpreted in a narrow sense, ….. a range of different molecular technologies such as gene manipulation and gene transfer, DNA typing and cloning of plants and animals” (FAO’s statement on biotechnology)

Biotic factor Other living organisms that are a component of an organism’s environment, and form the biotic environment, affecting the organism in many ways.

Blood pressure The pressure of blood against the main arteries.

Blot As a verb, to transfer DNA, RNA or protein to an immobilizing matrix. As a noun, the immobilizing matrix carrying DNA, RNA or protein. The various types of blot are named according to the probe and/or the probed molecules: Southern blot (DNA/DNA), northern blot (DNA/mRNA), western blot (antibody/protein), southwestern blot (DNA/protein). Only “Southern” is written with an initial capital, as it is named after Ed Southern, the inventor of the technique.

Breeding The process of sexual reproduction and production of offspring.

Broad-spectrum Describes an agent, such as an herbicide, that has a wide range of use.

Bt Abbreviation for Bacillus thuringiensis.

Bt-toxin Proteins produced by Bacillus thuringiensis (a group of soil bacteria). These proteins are called “cry” proteins, and are toxic to insects. When the DNA coding for “cry” proteins is inserted into the genomes of crop plants, the crop becomes resistant to insects.

By-product An incidental or secondary product made in the manufacture of a primary product.


Capsid The protein coat of a virus. The capsid often determines the shape of the virus.

Carcinogen A substance capable of inducing cancer in an organism.

Carotenoid A group of chemically similar red to yellow pigments responsible for the characteristic colour of many plant organs or fruits, such as tomatoes, carrots, etc. Oxygen-containing carotenoids are calledxanthophylls. Carotenoids serve as light-harvesting molecules in photosynthetic assemblies and also play a role in protecting prokaryotes from the deleterious effects of light.

Carrier A heterozygous individual bearing a recessive mutant allele for a defective condition that is “masked” by the presence of the dominant normal allele; the phenotype is normal, but the individual passes the defective (recessive) allele to half of its offspring.

Catabolic pathway A pathway by which an organic molecule is degraded in order to release energy for growth and other cellular processes.

Catabolism The breakdown of large molecules in living organisms, with the accompanying release of energy.

Catalysis The process of increasing the rate of a chemical reaction by the addition of a substance that is not itself changed by the reaction (thecatalyst).

Catalyst A substance that promotes a chemical reaction by lowering the activation energy of a chemical reaction, without itself undergoing any permanent chemical change.

cDNA Abbreviation for complementary DNA.

Cell The fundamental level of structural organization in complex organisms. Eukaryotic cells containa nucleus (with chromosomes) and cytoplasm with the protein synthesis machinery, bounded by a membrane. Prokaryotic cells have no nucleus.

Cell culture The in vitro growth of cells isolated from multi-cellular organisms.

Cell cycle The sequence of stages that a cell passes through between one division and the next. The cell cycle oscillates between mitosis (M) and the interphase, which is divided into the G1 phase (involving a high rate of biosynthesis and growth), the S phase (in which the DNA content is doubled as a consequence of chromosome replication), and the G2 phase (preparatory for cell division).

Cell differentiation The transition of cells (by the programmed activation and de-activation of the necessary genes) from an tissue-unspecific type, in which daughter cells are similarly undifferentiated, to a committed type in which the cell line specializes to become a recognizable tissue or organ.

Cell division Formation of two or more daughter cells from a single parent cell. The nucleus divides first, followed by the formation of a cell membrane between the daughter nuclei. Division of somatic cells is termed mitosis; egg and sperm precursors are formed following meiosis.

Cell fusion Formation in vitro of a single hybrid cell from the coalescence of two cells of different species origin. In the hybrid cell, the donor nuclei may remain separate, or may fuse, but during subsequent cell divisions, a single spindle is formed so that each daughter cell has a single nucleus containing complete or partial sets of chromosomes from each parental line.

Cell membrane The lipid bilayer and associated proteins and other molecules that surrounding the protoplast, within the cell wall.

Cell plate The precursor of the cell wall, formed at the beginning of cell division. The cell plate develops in the region of the equatorial plate and arises from membranes in the cytoplasm.

Cell sap Water and dissolved substances, sugar, amino acids, waste substances, etc., in the plant cell vacuole.

Cell suspension Cells in culture in moving or shaking liquid medium, often used to describe suspension cultures of single cells and cell aggregates.

Cell wall A rigid external structure which surrounds plant cells. It is formed outside the plasmalemma and consists primarily of cellulose.

Cellulase Enzyme catalysing the breakdown of cellulose.

Cellulose A complex polysaccharide composed of long linear chains of glucose residues. It comprises 40% to 55% by weight of the plant cell wall.

Centrifugation Separating molecules by size or density using centrifugal forces generated by a spinning rotor. G-forces of several hundred thousand times gravity are generated in ultracentrifugation.

Centrifuge A mechanical device which delivers the centrifugal forces necessary for centrifugation.

Centriole An organelle in many animal cells that appears to be involved in the formation of the spindle during mitosis. During cell division, the two centrioles move to opposite sides of the nucleus to form the ends of the spindle.

Centromere The eukaryotic chromosome structure, which appears as a constriction in karyotype analysis, to which the spindle fibres attach during mitotic and meiotic division. Composed of highly repetitive DNA.

Centrosome A specialized region of a living cell, situated next to the nucleus, where microtubules are assembled and broken down during cell division. The centrosome of most animal cells contains a pair of centrioles.

Chakrabarty decision A landmark legal case in the U.S.A., in which it was held that the inventor of a new micro-organism whose invention otherwise met the legal requirements for obtaining a patent, could not be denied a patent solely because the invention was alive. This has set the precedent for the patenting of life forms.

Chemical metabolism genes (CYP 2D6) Genes which code for enzymes governing the metabolism of chemical compounds in the body. Also see Genes, Enzymes and Metabolism.

Chemotaxis The movement of a cell, or the whole or part of an organism, towards or away from an increasing concentration of a particular substance.

Chemotherapy The treatment of disease, especially infections or cancer, by means of chemicals.

Chiasma A visible point of junction between two non-sister chromatids of homologous chromosomes during the first meiotic prophase.

Chimera 1. An organism whose cells are not all genotypically identical. This can occur as a result of: somatic mutation; grafting; or because the individual is derived from two or more embryos or zygotes. 2. A recombinant DNA molecule that contains sequences from different organisms.

Chlorenchyma Plant tissue (leaf mesophyll and other parenchyma cells) containing chloroplasts.

Chlorophyll One of the two pigments responsible for the green colour of most plants. It is an essential component of the machinery to absorb light energy for photosynthesis.

Chloroplast Specialized plastid that contains chlorophyll. Lens-shaped and bounded by a double membrane, chloroplasts contain membranous structures (thylakoids) piled up into stacks, surrounded by a gel-like matrix (stroma). They are the site of solar energy transfer and some important reactions involved in starch or sugar synthesis. Chloroplasts have their own DNA; these genes are inherited only through the female parent, and are independent of nuclear genes.

Chromatid Each of the two strands of chromatin comprising a duplicated chromosome. The term is applied only while the two chromatids are joined at the centromere. As soon as the centromere divides, setting the two chromatids adrift (during anaphase of mitosis; and during anaphase II of meiosis), they are called chromosomes.

Chromatin Substance of which eukaryotic chromosomes are composed. It consists of a complex of DNA, histone and non-histone chromosomal proteins (mainly histones), and a small amount of RNA.

Chromatin fibre The standard structural conformation of chromatin in strands of 30 nm average diameter.

Chromatography A method for separating the components of mixtures of molecules by partitioning them between two phases, one stationary and the other mobile. Appropriate selection of partitioning mechanism can produce separation of very closely-related molecules.

Chromosomal integration site A chromosomal location where foreign DNA can be integrated, often without impairing any essential function in the host organism.

Chromosome In eukaryotic cells, chromosomes are the nuclear bodies containing most of the genes largely responsible for the differentiation and activity of the cell. Chromosomes are most easily studied in their contracted state, which occurs around the metaphase of mitosis or meiosis; they contain most of the cell’s DNA in the form of chromatin. Each eukaryotic species has a characteristic number of chromosomes. Bacterial and viral cells contain only one chromosome, which consists of a single or double strand of DNA or, in some viruses, RNA, without histones.

Chromosome banding Differential staining of chromosomes in such a way that light and dark areas occur along the length of the chromosomes in repeatable patterns. Identical banding pattern implies chromosome homology.

Chromosome mutation A change in the gross structure of a chromosome, usually causing severely deleterious effects in the organism, but can be maintained in a population. They are often due to meiotic errors. The main types of chromosome mutation are translocation, duplication, s and inversion.

Chronic obstructive pulmonary disease General term that refers to two diseases of the lung – chronic bronchitis and emphysema. Also known as chronic obstructive lung disease.

Clinical trials Study involving human participants that is intended to discover or verify the effects of a drug for use in humans, to identify any adverse events in respect of a drug or to study the absorption, distribution, metabolism and excretion of a drug, with the objective of ascertaining its safety or efficacy.

Clone 1. A group of cells or individuals that are genetically identical as a result of asexual reproduction, breeding of completely inbred organisms, or forming genetically identical organisms by nuclear transplantation. 2. Group of plants genetically identical in which all are derived from one selected individual by vegetative propagation. 3. Verb: to clone. To insert a DNA segment into a vector or host chromosome.

Cloning vector A small, self-replicating DNA molecule – usually a plasmid or viral DNA chromosome – into which foreign DNA is inserted in the process of cloning genes or other DNA sequences of interest. It can carry inserted DNA and be perpetuated in a host cell.

Coccus A spherical bacterium.

Coding sequence That portion of a gene which directly specifies theamino acid sequence of its product. Non-coding sequences of genes include introns and control regions, such as promoters, operators, and terminators.

Coding strand The strand of aDNA double helix that contains the same base sequence (after substituting U for T) found in the mRNA molecule resulting from transcription of that segment of DNA. Sometimes called the sense strand. The mRNA molecule is transcribed from the other strand, known as the template or antisense strand.

Co-dominance Where both alleles are expressed in the heterozygous state, so that the phenotype reflects a contribution from both alleles. For example, roan coat colour in cattle results from a mixture of red hairs and white hairs, caused by heterozygosity for the red allele and the white allele.

Codon One of the groups of three consecutive nucleotides in mRNA, which represent the unit of genetic coding by specifying a particular amino acid during the synthesis of polypeptides in a cell. Each codon is recognized by a tRNA carrying a specific amino acid, which is incorporated into a polypeptide chain during protein synthesis. In DNA, any informative triplet of bases, including both coding and control sequences. See: genetic code, start codon, stop codon.

Co-enzyme Synonym for co-factor.

Co-factor An organic molecule or inorganic ion necessary for the normal catalytic activity of an enzyme. Synonym: co-enzyme.

Cold hardy Ability to grow in cold temperatures or resistant to cold weather damage.

Collagen A fibrous protein found in skin, tendons, ligaments, cartilage, and bones.

Collenchyma A tissue of living cells, found particularly in midribs and leaf petioles. Characterized by cell walls unevenly thickened with cellulose and hemicellulose, but never lignified; it functions as a mechanical support in young, short-lived or non-woody organs.

Colony 1. An group of genetically identical cells or individuals derived from a single progenitor. 2. A group of interdependent cells or organisms.

Complementary DNA (Abbreviation: cDNA). A DNA strand synthesized in vitro from a mature RNA template using reverse transcriptase. DNA polymerase is then used to create a double-stranded molecule. Differs from genomic DNA by the absence of introns. Synonym: copy DNA.

Complementary strands of RNA/DNA Complementary RNA (called nuclear RNA) is made when cells are making proteins from genes. It is made from the single-stranded DNA code and eventually changed into messenger RNA (mRNA). The mRNA carries its coded message to another part of the cell where it is translated into proteins. Complementary DNA (cDNA) is an artificial DNA made in the lab from mRNA strands, and is often used as probes. Also see RNA.

Confined field trials The release of novel organisms under terms and conditions of confinement such as reproductive isolation, site-monitoring and restrictions on use of the post experimental environment.

Conjugation 1. Union of gametes or unicellular organisms during fertilization. 2. The unidirectional transfer of plasmid DNA from one bacterium cell to another, involving cell-to-cell contact. The plasmid usually encodes the majority of the functions necessary for its own transfer. 3. Attachment of sugar and other polar molecules to less polar compounds, thus making them more water soluble.

Consanguinity Related by descent from a common ancestor.

Containment Measures and protocols applied to limit contact ofgenetically modified organisms or pathogens with the external environment.

Contaminant 1. An undesired chemical present in a compound or mixture of compounds. 2. Any micro-organism accidentally introduced into a culture or culture medium. The contaminant may compete with the desired cells and consequently inhibit their growth, or totally replace them.

Continuous cropping The growing of two or more crops, one after the other, on the same land in one growing season. Also known as succession cropping.

Controlled environment A closed environment in which parameters, such as light, temperature, relative humidity and sometimes the partial gas pressure (and possibly its composition), are fully controlled.

Co-suppression A naturalgene silencing phenomenon, which probably evolved as part of plants’ defence against viral attack, but which has become important in the context of plant transgenesis. Operates by inhibiting the expression of transgenes with homology to native DNA through the interaction of native and transgenic mRNA.

Cotyledon Leaf-like structures at the first node of the seedling stem. In some dicotyledons, they represent a food storage organ for the germinating seedling.

Coupling The phase state in which either two dominant or two recessive alleles of two different genes occur on the same chromosome.

Crohn’s disease An autoimmune disease involving the gastrointestinal tract. Also see Autoimmune diseases.

Crop rotation The practice of growing several different crops on the same land in successive years or seasons. Usually practised to replenish soil, and curb pests and diseases.

Cross The mating of two individuals or populations.

Cross hybridization The annealing of a single-strandedDNA sequence to a single-stranded target DNA to which it is only partially complementary. Often, this refers to the use of a DNA probe to detect homologous sequences in species other than the origin of the probe.

Cross pollination Application of pollen from one plant to another to effect the latter’s fertilization.

Cross-breeding Mating between members of different populations (lines, breeds, races or species).

Crossing over The process by which homologous chromosomes exchange material at meiosis through the breakage and reunion of non-sister chromatids. See: recombination, chiasma.

Cry proteins A class of crystalline proteins produced by strains of Bacillus thuringiensis, and engineered into crop plants to give resistance against insect pests. These proteins are toxic to certain categories of insects (e.g. corn borers, corn rootworms, mosquitoes, black flies, armyworms, tobacco hornworms, some types of beetles, etc.), but are harmless to mammals and most beneficial insects.

Cryogenic At very low temperature.

Culture A population of plant or animal cells or micro-organisms grown under controlled conditions.

Culture medium Any nutrient system for the cultivation of cells, bacteria or other organisms; usually a complex mixture of organic and inorganic nutrients.

Curing The elimination of a plasmid from its host cell. Many agents which interfere with DNA replication, e.g. ethidium bromide, can cure plasmids from either bacterial or eukaryotic cells.

Cuticle Layer of cutin or wax, formed on the outer surface of leaves and fruits, thought to have evolved to reduce evaporative water loss.

Cutting A detached plant part that, with appropriate treatment, can regenerate into a complete plant.

Cyclic adenosine monophosphate (Abbreviations: cyclic AMP, cAMP). A “messenger” molecule that regulates many intracellular reactions by transducing signals from extracellular growth factors to cellular metabolic pathways.

Cyclic AMP Abbreviation for cyclic adenosine monophosphate.

Cytochrome A class of pigments in plant and animal cells, usually in the mitochondria. They function as electron carriers in respiration.

Cytochrome p450 A highly diversified set (more than 1500 known sequences) of heme-containingproteins. Frequently called hydroxylases, although P450 proteins can perform a wide spectrum of other reactions. In bacteria they are soluble and approximately 400 amino acids long; eukaryotic P450s are larger – about 500 amino acids. In mammals they are critical for drug metabolism, haemostasis, cholesterol biosynthesis and steroidogenesis; in plants they are involved in plant hormone synthesis, phytoalexin synthesis, flower petal pigment biosynthesis and many unknown functions. In fungi they make ergosterol and they are involved in pathogenesis. Bacterial P450s are key elements in antibiotic synthesis.

Cytogenetics The biology of chromosomes and their relation to the transmission and recombination of genes.

Cytokine A generic name for a diverse group of soluble proteins and peptides which act as humoral regulators at extremely small concentrations and which, either under normal or pathological conditions, modulate the functional activities of individual cells and tissues.

Cytokinesis Cytoplasmic division and other changes exclusive of nuclear division that are a part ofmitosis or meiosis.

Cytoplasm The living material of the cell, exclusive of the nucleus, consisting of a complexprotein matrix or gel, and where essential membranes and cellular organelles (mitochondria, plastids, etc.) reside.

Cytoplasmic organelles Discrete sub-cellular structures located in the cytoplasm of cells – mitochondria, plastids and lysosomes.

Cytosine (Abbreviation: C). One thebases found in DNA and RNA.


Death phase The final growth phase of cell culture, during which nutrients have been depleted and cell number decreases.

Decode To spell-out the sequences of DNA and proteins into their basic units.

Definite diagnosis The diagnosis of a condition based on the unique characteristics of that condition. Definite diagnosis is difficult for conditions that share symptoms with other conditions.

Dehydrogenase An enzyme that catalyses the removal of hydrogen atoms in biological reactions.

Dehydrogenation A chemical reaction in which hydrogen is removed from a compound.

Deletion A mutation involving the removal of one or more base pairs in a DNA sequence. Large deletions are sometimes microscopically visible in karyotype analyses.

Denature To disrupt the normal in vivo conformation of a nucleic acid or (more usually) a protein by physical or chemical means, usually accompanied by the loss of activity.

Denatured DNA Double-stranded DNA that has been converted to single strands by breaking the hydrogen bonds linking complementary nucleotide pairs. Often reversible. Usually achieved by heating.

Denatured protein Altering the in vivo conformation of a protein by heat or salt treatment, thereby destroying its biological activity. Unlike denatured DNA, denatured proteins are seldom able to be renatured.

Derivative 1. Resulting from or derived from. 2. Term used to identify a variant during meristematiccell division.

Determinate growth Growth determined and limited in time, with a bud or flower terminating the growth of the main axis. Once established, it is usually irreversible.

Deviation 1. An alteration from the typical form, function or behaviour. Mutation or stress are the common reasons behind deviation. 2. A statistical term describing the difference between an actual observation and the mean of all observations.

Dicotyledon A plant with twocotyledons. One of the two major classes of flowering plants (along with the monocotyledons). Examples include many crop plants (potato, pea, beans), ornamentals (rose, ivy) and timber trees (oak, beech, lime).

Differentiation A process as a result of which unspecialized cells develop structures and functions characteristic of a particular type of cell, typically during the process of development from one cell to many cells, accompanied by a modification of the new cells for the performance of particular functions. The process is generally irreversible in vivo in higher organisms. In tissue culture, the term is used to describe the formation of different cell types.

Diploid The status of having two complete sets of chromosomes, most commonly one set of paternal origin and the other of maternal origin. Somatic tissues of higher plants and animals are ordinarily diploid in chromosome constitution, in contrast with the haploid gametes.

Disease resistance The genetically determined ability to prevent the reproduction of a pathogen, thereby remaining healthy. Some resistances operate by pathogen exclusion, some by preventing pathogen spread, and some by tolerating pathogen toxin.

Distillation The process of heating a mixture to separate the more volatile from the less volatile parts, and then condensing fractions of the resulting vapour so as to produce a more nearly pure or refined substance.

Dizygotic twins Two-egg twins, i.e. a pair of individuals that shared the same uterus at the same time, but which arose from separate and independent fertilization of two ova.

DNA Abbreviation for deoxyribonucleic acid, former spelling desoxyribonucleic acid. A long chain polymer of deoxyribonucleotides. DNA constitutes the genetic material of most known organisms and organelles, and usually is in the form of a double helix, although some viral genomes consist of a single strand of DNA, and others of a single- or a double-stranded RNA.

DNA amplification Many-fold multiplication of a particular DNA sequence either in vivo in a plasmid, phage or other vector; or in vitro using, most commonly, the polymerase chain reaction.

DNA cloning The process of creating exact copies of a DNA strand using various technologies.

DNA fingerprint A description of the genotype of an individual from the pattern of DNA fragments obtained from DNA fingerprinting. Synonym: DNA profile.

DNA fingerprinting The derivation of unique patterns of DNA fragments obtained using a number of marker techniques; historically these were RFLPs, but latterly they are generally polymerase chain reaction based. Synonym: genetic fingerprinting.

DNA helicase An enzyme that catalyses the unwinding of the complementary strands of a DNA double helix.

DNA probe Strands of DNA used to search for, and highlight, specific sequences of DNA in a sample. They can contain complementary strands of DNA and/or radioactive markers.

DNA repair A variety of mechanisms that repair errors (e.g. the incorporation of a non-complementary nucleotide) that occur naturally during DNA replication.

DNA replication The process whereby DNA copies itself, under the action of and control of DNA polymerase.

DNA sequencing Procedures for determining the nucleotide sequence of a DNA fragment. Two common methods available: 1. The Maxam Gilbert technique, which uses chemicals to cleave DNA into fragments at specific bases; or, most commonly, 2. the Sanger technique (also called the di-deoxy or chain-terminating method) which uses DNA polymerase to make new DNA chains, in the presence of di-deoxynucleotides (chain terminators) to stop the chain randomly as it grows. In both cases, the DNA fragments are separated according to length by polyacrylamide gel electrophoresis, enabling the sequence to be read directly from the gel. The procedure has become increasingly automated and large-scale in recent years.

DNA sequence The order of nucleotides that make up a given segment of a DNA molecule.

Dolly The first mammal (a sheep) to be created (via nuclear transfer) by the cloning of an adult cell (from the mammary tissue of a ewe). This showed that the process of differentiation into adult tissue is not, as previously thought, irreversible.

Dominance The gene action exhibited by a dominant allele.

Dominant 1. Of alleles, one whose effect with respect to a particular trait is the same in heterozygotes as in homozygotes. The opposite is recessive. 2. Of an individual animal, one that is allowed priority in access to food, mates, etc., by others of its species because of its success in previous aggressive encounters. 3. Of an animal or plant species, the most conspicuously abundant and characteristic in a particular location or environment.

Double crossing-over The formation of two chiasmata within a chromosome arm, leading to the generation of a double recombinant gamete with respect to genes located within the segment defined by the two genes concerned.

Double helix Describes the coiling of the two strands of the double-stranded DNA molecule, resembling a spiral staircase in which the base pairs form the steps and the sugar-phosphate backbones form the rails on each side. One strand runs 3′ to 5′, while the complementary one runs 5′ to 3′.

Double recessive An organism homozygous for a recessive allele at each of two loci.

Double-stranded complementary DNA A double-stranded DNA molecule created from a cDNA template.

Double-stranded DNA Two complementary strands of DNA annealed in the form of a double helix. Synonym: duplex DNA.

Drosophila melanogaster The fruit fly, used for many years as a model for eukaryotic genetics. Of the nearly 300 disease-causing genes in the human genome, more than half have an analogous gene in the Drosophila genome.

Drug delivery Method by which a drug is delivered to its site of action. For traditional drugs this is another name for formulation. However, biotechnology has allowed the development of a range of new therapeutic-agent delivery systems, such as liposomes and other encapsulation techniques, and a range of mechanisms that target a therapeutic agent to a particular cell or tissue.

Dry weight The weight of tissue obtained following sufficiently prolonged oven-drying at high temperature to remove all water. Freeze-drying may also be employed but generates a slightly different result because bound water is not removed.

Drug metabolism The process by which enzymes break down drugs into different chemical components. The breakdown allows the drug to carry out its therapeutic role and eventually be eliminated from the body.

Drug resistance A condition in which disease-causing microorganisms develop an ability to tolerate drugs, which were once effective against them. Results in the loss of effectiveness in a drug.

Duplication Multiple occurrence of: 1. A DNA sequence within a defined length of DNA; or 2. A specific segment in the same chromosome or genome.


Ecosystem The complex of a living community and its environment, functioning as an ecological unit in nature.

Ecozones Large, generalized ecologically distinctive areas that are distinguished based on the interplay of landform, water, soil, climate, plants, and human factors.

Effector molecule A molecule that influences the behaviour of a regulatory molecule, such as arepressor protein, thereby influencing gene expression.

Egg 1. The fertilized zygote in egg-laying animals. 2. The mature female reproductive cell in animals and plants.

Electro-blotting The electrophoretic transfer ofDNA, RNA or protein from a gel, in which they have been separated, to a support matrix, such as nitrocellulose. A transfer technique employed in Southern and northern blotting.

Electrophoresis A ubiquitous molecular biology technique, with many variants, used to resolve complex mixtures of macromolecules into their components. Its principle is to subject samples to an electric field applied across a porous matrix. Molecules will migrate under these conditions at a rate dependent on their net electric charge and/or their molecular weight.

Electroporation The induction of transient pores in bacterial cells or protoplasts by the application of a pulse of electricity. These pores allow the entry of exogenous DNA into the cell. Widely used for the transformation of bacteria.

Embryo An immature organism in the early stages of development. In mammals, develops in the first months in the uterus. In plants, it is the structure that develops in the megagametophyte, as result of the fertilization of an egg cell, or occasionally without fertilization. Somatic embryos can often be induced in in vitro plant cell cultures.

Embryo splitting The splitting of young embryos into several sections, each of which develops into an animal. A form of animal cloning, i.e. of producing animals that are genetically identical. In practice, the number of animals that can be produced from a single embryo is less than 10.

Embryo storage Cryogenic preservation of animal embryos, allowing inembryonation or other manipulations long after embryo formation.

Embryogenesis 1. (General) Development of an embryo. 2. (In plants) In vitro formation of plants from plant tissues, through a pathway closely resembling normal embryogeny from the zygote. Somatic cell embryogenesis is an alteRNAtive technique. The generation of embryos has two stages: initiation and maturation. Initiation needs a high level of the group of plant hormones called auxins; maturation needs a lower level.

Embryonic stem (ES) cells Cells of the early embryo that can give rise to all differentiated cells, including germ line cells.

Endocytosis The process by which materials enter a cell without passing through the cell membrane. The membrane folds around material outside the cell, resulting in the formation of a sac-like vesicle inside which the material is entrapped. This vesicle is then pinched off from the cell surface so that it lies within the cell.

Endocrine glands Any gland in the body that secretes hormones into the blood. There are five major endocrine glands in the human body: the pituitary, the gonads, the adrenals, the thyroid, and the parathyroids.

Endocytosis A process that some cells use to bring material into the cell without having it pass through the cell membrane. Instead, the cell membrane folds around the material outside the cell to form a sac, and incorporates the sac into the body of the cell.

Environmental toxicology assessment A measurement of a toxin in a given area. For example, testing drinking water for arsenic levels.

Enzyme A protein that acts as a catalyst in biochemical reactions. They are produced by living cells.

Enzyme Linked Immunoabsorbent Assay (ELISA) A lab test that can give a simple positive or negative result for a protein using the complementary relationship of antigens and antibodies.

Epidemic A widespread incident of a disease in a specific area at a particular time.

Epidemiology The study of disease incidence, distribution, control, and prevention in the population.

Erucic acid An organic acid produced by some plants. Has applications in industry, but is toxic to humans.

Essential component Chemical compounds that are required for life, growth, and tissue repair.

Essential fatty acid A group of polyunsaturated fatty acids, such as linoleic acid, that must be included in a mammal’s diet.

Evaluators Officers from a regulatory agency, responsible for carrying out assessments and enforcing the acts and regulations of that particular agency.

Expression/expressed Describes the process that converts the gene’s coded information into the structures present and operating in the cell.


F1 Abbreviation for filial generation 1. The initial hybrid generation resulting from a cross between two parents.

F2 The second hybrid generation, produced either by intercrossing two F1 individuals, or by self-fertilizing an F1 individual.

Facultative anaerobe An organism that will grow under either aerobic or anaerobic conditions.

Familiar(ity) The knowledge of the characteristics of a given organism and experience with the use of that organism in Canada.

Fatty acids A variety of monobasic acids derived from animal and vegetable fats and oils. They are used in cooking and food engineering, and in the production of soaps, detergents, and cosmetics.

Feedback inhibition The process by which the accumulated end product of a biochemical pathway stops synthesis of that product. The effect is that a late metabolite of a synthetic pathway regulates the synthesis of an earlier step of the pathway. See: end-product inhibition.

Feed conversion A productivity measure of an animal. Defined as the ratio of feed consumed to weight gained.

Feedstock(s) Raw material(s) used for the production of chemicals.

Fermentation The anaerobic breakdown of complex organic substances, especially carbohydrates, by micro-organisms, yielding energy. Often misused to describe large-scale aerobic cell culture in specialized vessels (fermenters, bioreactors) for secondary product synthesis.

Fermentation substrates Materials used as food for growing micro-organisms. The fermentation substrates and the trace materials needed, together with chemicals added to make the fermentation easier, form the culture medium.

Fertilization The union of two gametes from opposite sexes to form a zygote. Typically, each gamete contains a haploid set of chromosomes. Hence the zygotic nucleus contains a diploid set of chromosomes. Several categories can be distinguished: 1. Self-fertilization (selfing): fusion of male and female gametes from the same individual. 2. Cross-fertilization (crossing): fusion of male and female gametes from different individuals. 3. Double fertilization; restricted to flowering plants, in which the fusion of one male gamete with the ovum occurs at about the same time as the second male gamete nucleus fuses with the female polar nuclei (or secondary nucleus) to form the endosperm.

Fertilizer Any substance that is added to soil in order to increase its productivity. Fertilizers can be of biological origin (e.g. composts), or they can be synthetic (artificial fertilizer).

Field selection trait Observable characteristics which make it possible to select certain varieties of an organism from a group of them grown in their natural habitat.

Field trials An experimental trial of plant species grown at a specific trial site for the purposes of conducting research. Can also apply to environmental products, such as pesticides. The trial can be unconfined or confined.

Fission Asexual reproduction involving the division of a single-celled individual into two daughter single-celled individuals of approximately equal size.

Fitness The survival value and the reproductive capability of an individual, compared to that of competitor individuals of the same or other species within a population or an environment.

Fixation The situation in which only one allele for a given gene/locus is present in a population. This can occur as a result of direct selection where the allele delivers a greater level of fitness; because of indirect selection, where the locus is linked to a gene that is subject to direct selection; or because of genetic drift.

Flaming A technique for sterilizing instruments, to remove live micro-organism contaminants. The instrument is dipped in alcohol, and the alcohol remaining on the instrument is ignited, thereby heat-sterilizing the surface.

Flanking region The DNA sequences extending either side of a specific sequence.

Flocculant A chemical agent that causes small particles to aggregate (flocculate).

Floccule A micro-organism aggregate or colloidal particle floating in or on a liquid. The cloudy appearance of micro-organism contaminated liquid media illustrates the flocculation phenomenon.

Fluorescence immunoassay (Abbreviation: FIA). An immunoassay based on the use of fluorescence-labelled antibody.

Fluorescence in situ hybridization (Abbreviation: FISH). Hybridization of cloned, fluorescently labelled DNA or RNA, to intact biological materials, notably chromosome spreads and thin tissue sections. The technique allows the visualization of the physical location of nucleic acid sequences homologous to the probe, and is used for the placement of genes on chromosomes and for the spatial and temporal pattern of gene expression of specific mRNA molecules.

Fluorescent probe A probe which is labelled with a fluorescent dye, so that the signal emitted can be captured by photometric methods.

Follicle An enclosing cluster of cells that protects and nourishes a cell or structure within. Thus a follicle in the ovary contains a developing egg cell, while a hair follicle envelops the root of hair.

Follicle stimulating hormone (Abbreviation: FSH). A hormone, secreted by the anterior pituitary gland in mammals, that stimulates the ripening of the specialized structures in the ovary (Graafian follicles) that produce ova in female mammals; and in males, the formation of sperm in the testis. FSH is a major constituent of fertility drugs.

Forward mutation A mutation from the wild type to the mutant type. Opposite: reverse mutation.

Frameshift mutation A mutation that changes the reading frame of a DNA, either by the insertion or the deletion of nucleotides. Because of the triplet nature of codons, this occurs if the number of nucleotides involved is not a multiple of three.

Fresh weight The weight, including the water content, of a specimen. Synonym: wet weight.

Functional genomics The field of research, that aims to determine patterns of gene expression and interaction in the genome, based on the knowledge of extensive or complete genomic sequence of an organism.

Fungicide A chemical agent toxic to fungi.

Fungus/fungi Multinucleate single-celled or multicellular heterotrophic micro-organisms, including yeasts, moulds, and mushrooms. They live as parasites, symbionts, or saprophytes. Lacking any vascular tissues (unlike plants), their cell walls are made of chitin or other non-cellulose compounds.


Gamete A mature reproductive cell which is capable of fusing with a cell of similar origin but of opposite sex to form a zygote from which a new organism can develop. Gametes normally have a haploid chromosome content. In animals, a gamete is a sperm or egg; in plants, it is pollen, spermatic nucleus, or ovum.

Gametogenesis The process of the formation of gametes.

Gametophyte The phase of the plant life cycle that carries the gamete producing organs. In flowering plants, the pollen grain is the male gametophyte and the embryo sac is the female gametophyte.

Gastrula An early animal embryo consisting of two layers of cells; an embryological stage following the blastula.

Gel A jelly-like solid, used widely as a matrix for the electrophoresis of macromolecules, for encapsulation, and to solidify media for cell cultures.

Gel electrophoresis See: electrophoresis.

Gel filtration A method ofprotein or DNA purification, where differences in size are used to separate the components of a complex mixture.

Gene The unit of heredity transmitted from generation to generation during sexual or asexual reproduction. More generally, the term is used in relation to the transmission and inheritance of particular identifiable traits. The simplest gene consists a segment of nucleic acid that encodes an individual protein or RNA.

Genetics The branch of biology concerned with heredity. It is the study of how genes operate and are passed on from parents to offspring.

Gene cloning The synthesis of multiple copies of a chosenDNA sequence using a bacterial cell or another organism as a host. The gene of interest is inserted into a vector, and the resulting recombinant DNA molecule is amplified in an appropriate host cell. Synonym: DNA cloning.

Gene expression The process by which a gene produces mRNA and protein, and hence exerts its effect on the phenotype of an organism.

Gene insertion The incorporation of one or more copies of a gene into a chromosome.

Gene interaction The modification of the action of one gene by another, non-allelic gene.

Genetic modification Chemical change to a gene’s DNA sequence.

Gene pool 1. The sum of all genetic information in a breeding population at a given time. 2. In plant genetic resources, use is made of the terms ‘primary’, ‘secondary’ and ‘tertiary’ gene pools. In general, members of the primary gene pool are inter-fertile; those of the secondary can be crossed with those in the primary gene pool under special circumstances; but to introgress variation from the tertiary gene pool, special techniques are required to achieve crossing.

Gene replacement The incorporation of a transgene into a chromosome at its normal location by homologous recombination, thus replacing the copy of the gene originally present at the locus.

Gene sequencing See: DNA sequencing.

Gene splicing See: splicing

Gene therapy The proposed treatment of an inherited disease by the transformation of an affected individual with a wild-type copy of the defective gene causing the disorder. In germ-line (or heritable) gene therapy, reproductive cells are transformed; in somatic-cell (or non-inheritable) gene therapy, cells other than reproductive ones are modified.

Gene tracking Following theinheritance of a particular gene from generation to generation.

Genetic code The correspondence between the set of 64 possible nucleotide triplets and the amino acids and stop codons that they specify.

Genetic complementation When two DNA molecules that are in the same cell together produce a function that neither DNA molecule can supply on its own.

Genetic disease A disease caused by an abnormality in the genetic material, which could be at the level of DNA sequence at a locus, or at the level of karyotype. Usually refers to inherited diseases, although somatic mutations can also cause disease without being inherited.

Genetic diversity The heritable variation within and among populations which is created, enhanced or maintained by evolutionary or selective forces.

Genetic drift Change in allele frequency from one generation to another within a population, due to the sampling of finite numbers of genes that is inevitable in all finite-sized populations. The smaller the population, the greater is the genetic drift, with the result that some alleles are lost, and genetic diversity is reduced. Thus minimization of genetic drift is an important consideration for conservation of genetic resources.

Genetic engineering Modifying genotype, and hence phenotype, by transgenesis.

Genetic information Information contained in anucleotide base sequence in chromosomal DNA or RNA.

Genetic map The linear array of genes on a chromosome, based on recombination frequencies (linkage map) or physical location (physical or chromosomal map).

Genetic marker A DNA sequence used to identify a particular location (locus) on a particular chromosome.

Genetics The science of heredity.

Genetic tags Genes of certain observable traits that are used as markers when introducing foreign genes into an organism. They are usually “tagged” onto the desired genes and indicate whether an organism has successfully incorporated those desired genes into its genome. The gene for antibiotic resistance is often used as a genetic tag. Also known as selectable markers.

Genetic testing This type of testing involves the examination of an individual’s DNA. Also known as gene testing and DNA testing.

Genome 1. The entire complement of genetic material (genes plus non-coding sequences) present in each cell of an organism, virus or organelle. 2. The complete set of chromosomes (hence of genes) inherited as a unit from one parent.

Genomics The research strategy that uses molecular characterization and cloning of whole genomes to understand the structure, function and evolution of genes and to answer fundamental biological questions.

Genotype 1. The genetic constitution of an organism. 2. The allelic constitution at a particular locus, e.g. Aa or aa. 3. The sum effect of all loci that contribute to the expression of a trait.

Germ cell A member of a celllineage (the germ line) leading to the production of gametes. In mammals, germ cells are found in the germinal epithelium of the ovaries and testes. Synonym: germ line cell.

Germ layer The layers of cells in an animalembryo at the gastrula stage, from which the various organs of the animal’s body will be derived.

Glial cells Cells of the nervous system that aid neurons. They provide nutrition for the neurons, and insulate them from each other. They make up 40 percent of the volume of the brain and spinal cord.

Glucosinolates A class of molecules produced in the seeds and green tissue of a range of plants, in particular brassicas. Their natural role is thought to be involved in plant-insect interactions. Their importance in plant breeding is largely because of their negative influence on taste and their positive effect on the prevention of cancers of the alimentary tract.

Glycolysis The sequence of reactions that converts glucose into pyruvate, with the concomitant production of ATP.

GM food Abbreviation for genetically modified food. Food that contains above a certain legal minimum content of raw material obtained from genetically modified organisms.

Golden rice A biotechnology-derived rice, which contains large amounts of beta carotene (a precursor of vitamin A) in its seeds. Achieved by inserting two genes from daffodil and one from the bacterium Erwinia uredovora.

Golgi apparatus An assembly of vesicles and folded membranes within the cytoplasm of plant and animal cells that stores and transports secretory products (such as enzymes and hormones) and plays a role in formation of a cell wall (when this is present).

Gonad One of the (usually paired) animal organs that produce reproductive cells (gametes). The most important gonads are the male testis, which produces spermatozoa, and the female ovary, which produces ova (egg cells). The gonads also produce hormones that control secondary sexual characteristics.

Good laboratory practice (Abbreviation: GLP). Written codes of practice designed to reduce to a minimum the chance of procedural or instrument problems which could adversely affect a research project or other laboratory work.

Good manufacturing practice (Abbreviation: GMP). Codes of practice designed to reduce to a minimum the chance of procedural or instrument/manufacturing plant problems which could adversely affect a manufactured product.

Graft 1. Verb. To place a detached branch or bud (scion) in close cambial contact with a rooted stem (rootstock) in such a manner that scion and rootstock unite to form a single plant. 2. Noun. Colloquial synonym for scion.

Gram staining A technique to distinguish between two major bacterial groups, based on whether or not their cell wall retains the Gram stain. Gram-positive bacteria are stained dark purple, while Gram-negative bacteria are only faintly coloured. Stain retention is determined by the structure of the cell wall.

Growth factor Any of various chemicals, particularly polypeptides, that have a variety of important roles in the stimulation of new cell growth and cell maintenance. They bind to the cell surface on receptors. Specific growth factors can cause new cell proliferation.

Growth hormone (Abbreviation: GH). A group of hormones, secreted by the mammalian pituitary gland, that stimulates protein synthesis and growth of the long bones in the legs and arms. They also promote the breakdown and use of fats as an energy source, rather than glucose. Synonym: somatotropin.

Guidelines Documents produced by the regulatory agencies to accompany the regulations and acts. They provide the steps an individual should follow with respect to a given act or regulation. They are not enforceable by law, but failure to follow them may result in actions contrary to an act or regulation, which is enforced by law.

Guthrie test A bacteria-based diagnostic test used to detect phenylketonuria (PKU) in newborns. The test measures concentrations of amino acids in a sample of blood.


Haemophilia A sex-linked hereditary bleeding disorder in which it takes a long time for the blood to clot and abnormal bleeding occurs. This disease affects mostly males.

Haploid A cell or organism containing one of each of the pairs of homologous chromosomes found in the normal diploid cell.

Hardy-Weinberg equilibrium The frequencies of genotypes at a locus resulting from random mating at that locus; for two alleles, A1 and A2, with respective frequencies in a population of p and q, the Hardy-Weinberg equilibrium frequencies are p2 A1A1; 2pq A1A2; q2 A2A2. Departure from these frequencies is an indication that random mating is not occurring.

Helix A structure with a spiral shape. The normal state of double-stranded DNA is in the form of a double helix.

Helminth A class of parasitic worms, especially those which are internal parasites of man and animals.

Helper cell T cells that assist in stimulating B and T lymphocytes to develop into antibody-producing plasma cells and killer T cells, respectively.

Hemizygous The condition in which genes are present only once in the genotype and not in pairs. Occurs for all genes in haploids, for all genes located in the differential segments of the sex chromosomes in diploids, and in various aneuploids and deletion mutant heterozygotes. Synonym: haplozygous.

Hemophilia See: haemophilia.

Heredity Resemblance among individuals related by descent; transmission of traits from parents to offspring.

Heritability The degree to which a given trait is controlled by inheritance, as opposed to being controlled by non-genetic factors.

Hermaphrodite 1. An animal that has both male and female reproductive organs, or a mixture of male and female attributes. 2. A plant whose flowers contain both stamen and carpels. Synonym: intersex.

Heterozygote An individual with non-identical alleles for a particular gene or genes. The condition is termed “heterozygous”. Opposite: homozygote.

High density lipoprotein A type of soluble protein that transports cholesterol back to the liver from peripheral cells.

Homeostasis The process by which the internal systems of the body maintain a balance, despite external conditions.

Homogenotization An allele replacement technique, in which a bacterial cell is transformed with a plasmid containing an altered copy of the target sequence, and a double recombination event effects the substitution of the wild type allele by the altered one. An antibiotic resistance gene is usually fused to the altered copy in the plasmid, so that double recombinants can be selected.

Homologous 1. General definition: from the same source, or having the same evolutionary function or structure. 2. Of chromosomes: identical with respect to gene content and linear ordering. Homologous chromosomes pair and recombine with one another at meiosis. 3. Of DNA/proteins: identical, or nearly identical nucleotide/amino acid sequence.

Homology 1. The degree of identity between individuals, or characters. 2. The degree of identity of sequence (nucleotide or amino acid) between a number of DNA or polypeptide molecules.

Honolulu technique A type of nuclear transfer used to clone mammals. It uses donor cells that stay dormant longer so that they do not have to undergo the extra step of being grown in a medium, as in the Roslin technique.

Hormone A specific chemical, produced in one part of a plant or animal body, and transported to another part where, at low concentrations, it promotes, inhibits or quantitatively modifies a biological process.

Host An organism that contains another organism or a cloning vector.

Human Leukocyte Antigen (HLA) The unique proteins on the cells beloning to one’s body. They distinguish the cells that blong to the body from those that do not. There are over 100 different HLAs.

Hybrid 1. The offspring of two genetically unlike parents. 2. Of DNA molecules, see: heteroduplex.

Hybrid somaclonal variant cell line The offspring of plant cells from cell cultures. They have enhanced genetic instability.

Hybrid vigour The extent to which a hybrid individual outperforms both its parents with respect to one or many traits. The genetic basis of hybrid vigour is not well understood, but the phenomenon is widespread, particularly ininbreeding plant species. Synonym: heterosis.

Hybridization 1. The process of forming a hybrid by cross pollination of plants or by mating animals of different types. 2. The production of offspring of genetically different parents, normally from sexual reproduction, but also asexually by the fusion of protoplasts or by transformation. 3. The pairing of two DNA strands, often from different sources, by hydrogen bonding between complementary nucleotides.

Hybridoma A synthetichybrid cell, derived by fusing a B lymphocyte with a tumour cell. The former secretes a single antibody, while the latter confers the property of growing indefinitely in tissue culture. The underlying technology behind the monoclonal antibody.

Hydrolase A group of enzymes that speeds up the process of hydrolysis.

Hydrolysis A chemical reaction in which water is added across a covalent bond, often cleaving the molecule into two. Occurs for example when polynucleotides, polypeptides, and polysaccharides are broken into their component monomers. Thus sucrose can be hydrolysed to glucose and fructose; and proteins to individual amino acids.

Hydrophobic interaction An interaction between a hydrophobic (‘water-hating’) part of a molecule and an aqueous environment. Particularly significant in establishing the conformation of molecules in solution, and thus their biological activity. Many enzymes have a structure where the polypeptide chain is folded to form a hydrophobic core and a hydrophilic (‘water-loving’) surface.

Hypothalamus Part of the brain that is responsible for regulating body temperature, water and food intake, and sleep. It is also responsible for regulating the release of hormones.


Ichthyosis A genetic skin disorder that causes abnormal scaling of the skin. There are several different forms of the disorder, each caused by a different genetic defect related to skin shedding.

Idiopathic Describes any disorder with unknown causes.

Immune response The processes, including the synthesis of antibodies, that are used by vertebrates to respond to the presence of a foreign antigen.

Immune system The group of cells, molecules, and organs in the body that act together to defend the body against foreign invaders that may cause disease.

Immunity The lack of susceptibility of an animal or plant to infection by a particular pathogen, or to the harmful effects of their toxins.

Immunoglobulins Type of blood protein used by the body against disease. They can bind specifically to foreign disease cells and particles, and activate the immune system.

Immunoassay An detection system for a particular molecule, which exploits the specific binding of anantibody raised against it. For measurement, the antibody can incorporate a radioactive or fluorescent label, or be linked to an enzyme which catalyses an easily monitored reaction such as a change in colour (see: ELISA).

Incompatibility 1. Genetically or physiologically determined prevention of intermating. 2. A physiological interaction resulting in graft rejection or failure. 3. A function of a related group of plasmids. Incompatible plasmids share similar replication functions, and this leads to the exclusion of one or the other plasmid if they are present in the same cell. Plasmids belonging to one incompatibility group are very closely related.

Incompatibility group Plasmids must belong to different incompatibility groups to co-exist within the same cell. Aplasmid cloning vector should always belong to an incompatibility group different from that of the host bacterium’s endogenous plasmids.

Incomplete dominance A gene action in which heterozygotes have a phenotype that is different from either homozygote, and is usually intermediate between them.

Incubation 1. The hatching of eggs by means of heat, either natural or artificial. 2. Period between infection and appearance of symptoms induced by a pathogen. 3. The culture of cells and organisms.

Incubator An apparatus in which environmental conditions (light, photoperiod, temperature, humidity, etc.) are fully controlled; used for hatching eggs, multiplying micro-organisms, culturing plants, etc.

Independent assortment The random distribution duringmeiosis of alleles (at different genes) to the gametes that is the case when the genes in question are located on different chromosomes or are unlinked on the same chromosome.

Industrial corn A variety of corn that is processed and used in livestock feeds, processed foods and industrial products.

Infection The successful colonization of any living organism by a pathogen.

Infectious agent Synonym of pathogen.

Infectivity The potential for a given micro-organism to cause an infection.

Inoculants Disease-causing organisms or infective agents that promote immunity against the disease when introduced (injected) into an organism or medium.

Inoculate Deliberately introduce, in contrast to contamination. 1. In bacteriology, tissue culture, etc., placing an inoculum into (or onto) medium to initiate a culture. 2. In immunology, to carry out immunization. 3. In plant pathology, application of pathogen spores etc. on to plants under conditions where infection should result in the absence of resistance.

Insertion mutation Changes in the base sequence of aDNA molecule resulting from the random integration of DNA from another source. See: mutation.

Insertion site 1. A unique restriction site in a vector DNA molecule into which foreign DNA can readily be inserted. This is achieved by treating both the vector and the insert with the relevant restriction endonuclease and then ligating the two different molecules, both having the same sticky ends. Synonym: cloning site. 2. The position of integration of a transposon.

in situ In the natural place or in the original place. 1. Experimental treatments performed on cells or tissue rather than on extracts from them. 2. Assays or manipulations performed with intact tissues.

in situ colony hybridization A procedure for screening bacterial colonies or plaques growing on plates or membranes for the presence of specific DNA sequences by the hybridization of nucleic acid probes to the DNA molecules present in these colonies or plaques. Synonym: in situ plaque hybridization.

in situ conservation The conservation of ecosystems and natural habitats and the maintenance and recovery of viable populations of species in their natural surroundings and, in the case of domesticated or cultivated species, in the surroundings where they have developed their distinctive properties.

in situ hybridization The visualization of in vivo location of macromolecules (particularly polynucleotides and polypeptides) by the histological staining of tissue sections or cytological preparations via labelled probes/antibodies.

Integrated pest management A variety of techniques and practices to minimize damage to crops caused by plant pests, while at the same time minimizing production costs and preserving the environment.

Intellectual property rights (Abbreviation: IPR). The legal framework, which includes patenting and plant variety protection, by which inventors control the commercial application of their work.

Interference The effect of one crossing over event in altering the probability of another crossing over event occurring at a nearby location. This probability can be either increased (positive interference) or decreased (negative interference), but the latter is the more usual.

International regulatory status The regulations that govern the acceptable uses of, and the tests performed on, a particular product in worldwide markets.

Interferon A protein which belongs to a class of immune system proteins called cytokines. It possesses potent antiviral characteristics.

Interleukins A group of proteins produced by cells of the immune system when stimulated by antigens.

Interphase The stage in the cell cycle when the cell is not dividing and during part of which DNA replication occurs; it follows telophase of one mitotic division and extends to the beginning of prophase in the next division.

Intracellular Occurring within a cell.

Intracytoplasmic sperm injection (Abbreviation: ICSI). The micro-injection of a single sperm into the cytoplasm of a mature oocyte.

Intravenous Describes fluids or medication administered directly into the vein.

Intron A segment of the primarytranscript of a eukaryotic gene, removed (before the mature mRNA is translated) in a process known as intron splicing. Some eukaryotic genes contain a large number of introns, which make up the bulk of the DNA sequence of the gene. Introns are also found in genes whose RNA transcripts are not translated, namely eukaryotic rRNA and tRNA genes. In these cases the intron sequence does not appear in the functional RNA molecule. Synonym: intervening sequence.

in vitro Outside the organism, or in an artificial environment. Applied for example to cells, tissues or organs cultured in glass or plastic containers.

in vitro fertilization (Abbreviation: IVF). A widely used technique in human and animal science, whereby the egg is fertilized with sperm outside the body before re-implanting into the uterus.

in vivo The natural conditions in which organisms reside. Refers to biological processes that take place within a living organism or cell under normal conditions.

Ion channel A protein integral to a cell membrane, through which selective ion transport occurs.

Islet cells Insulin-producing cells in the pancreas. If these cells are destroyed, Type I diabetes develops. Also known as beta cells.

Isomer 1. Structural isomers have the same chemical formula but different structures; e.g. leucine and isoleucine. 2. Stereoisomers are different topological forms of an otherwise single chemical structure, due to changes in bond configurations about some axis or plane of symmetry; eg, D- and L-glucose or cis- and trans-cinnamic acid.

Isomerase Any of a class of enzymes that catalyse the re-arrangement of the atoms within a molecule, thereby converting one isomer into another.

Isopentenyltransferase (IPT) selection system An alternative genetic tag to antibiotic resistance genes. IPT is an enzyme involved in plant growth hormone biosynthesis.

Isotope One of two or more forms of an element that differ in the number of neutrons carried by the nucleus. Radioactive isotopes (radio-isotopes) are used as probes in many biochemical analyses.