For additional terminology please refer to a glossary of recombinant DNA technology and genetic engineering by Lekh R. Batra, in “Public Perceptions of Biotechnology”, ed. by L.R. Batra & W. Klassen, Bethesda, Maryland: Agricultural Research Institute, 1987.
Agrobacterium: A bacterium with the ability to infect tissues, integrating, as it does so, part of its own DNA into that of the host. This characteristic renders Agrobacterium a useful vector for genetic engineering.
Allele: Any one of the alternative forms of a particular gene which may occur at a locus.
Allozyme: An isozyme which differs from other variants of the enzyme as a result of an allelic difference.
Anther: The part of the stamen which produces pollen.
Antisense: An antisense strand of a gene sequence will give rise to mRNA which is complementary to, and therefore will bind to, the product of the sense DNA strand. This prevents the sense transcript from being translated to a gene product.
Apomixis: A process of reproduction without fertilization.
Biolistic: Referring to methods which employ particle bombardment to introduce DNA into cells or protoplasts.
Bulked Segregant Analysis: Marker analysis applied to two bulked DNA samples prepared from individuals selected, in a segregating population, to be contrasting with respect to a trait of interest.
Catalytic: Accelerating a reaction.
cDNA: Copy DNA, prepared from mRNA using an enzyme called reverse transcriptase. The cDNA can then be used as a probe to locate the real gene by hybridisation.
Chimaera: A single organism made up of two or more genotypes.
Chiasma: Crossing over events at meiosis, resulting in gene recombination.
Chloroplast: A plastid (body) located within the plant cell, and in which photosynthesis takes place.
Chromatin: The nucleoprotein content of the cell nucleus.
Codominant: Where two alleles at a locus are expressed.
Colchicine: A plant-derived alkaloid with the capacity to interfere with the mitotic process, leading to polyploidy.
Construct: An artificially assembled DNA segment to be transferred into the target tissue. Typically, the construct will include the gene of particular interest, a marker gene, and appropriate control sequences.
Cryopreservation: Preservation of cells, organs or tissues by maintenance at very low temperatures, typically by immersion in liquid nitrogen.
Cryoprotectant: A chemical which, when applied to the cells or tissues to be cryopreserved, enhances their tolerance to the freezing process.
Cybrid: A hybrid cell or line formed by the fusion of cell parts from different individuals.
Cytoplasm: The living contents of a cell, other than the nucleus.
Dinucleotide: A segment of DNA comprising a pair of nucleotides.
Diploid: Having two sets of chromosomes, the most common zygotic number.
Dominant: Where one allele at a locus is expressed, while the other is masked.
DNA: Deoxyribonucleic acid. The self-replicating substance, existing primarily in the chromosomes, which contains all of the heriditary information.
Electrophoresis: The process by which charged particles move, typically through a gel, in response to an electric field.
Electroporation: The use of an electric current to alter membrane permeability, and thus allow e.g. DNA molecules to be introduced into a cell.
Embryogenesis: A process of differentiation which results in the formation of embryo-like structures from undifferentiated cells.
Enzyme: A catalytic protein.
Enzyme kinetics: Quantitative characteristics of enzymic reactions.
Epigenetic: Influencing the expression of genes, but not inherent in the genotype.
Eukaryote: Organisms whose DNA is organized into chromosomes, with a nuclear membrane.
Ex situ conservation: Conservation other than in in situ stands.
Explant: An organ, piece of tissue, or cell which is taken for culture.
Fingerprinting: The use of markers to unambiguously characterise a genotype.
Gamete: Haploid cell which, when combined with one of the opposite gender, gives rise to a zygote.
Gametophyte: The gamete-bearing body.
Gene: A segment of DNA giving rise to a particular enzymic product and having a particular effect on phenotype.
Genetic engineering: Techniques used to isolate, manipulate and transfer genes.
Genome: The complete genetic complement of an individual organism.
Haploid: Having a single set of chromosomes, typical of the gametophyte.
Heterosis: Hybrid vigour resulting from cross-fertilisation.
Heterozygous: With two different alleles at a locus, on the homologous chromosomes.
Homozygous: Where the two alleles at a locus are identical.
Hybridisation: In the context of DNA technology, this refers to the formation of a double stranded molecule by complementary base pairing between two single stranded molecules.
In situ conservation: Conservation in natural stands.
In vitro: Referring to processes taking place in culture in an artificial apparatus.
In vivo: Referring to processes taking place under natural conditions.
Introgression: Gradual diffusion of genes from one population to another through hybridization.
Isozyme: A variant of a particular enzyme, detectable generally in terms of molecular size, shape, and charge.
Linkage: The tendency for genes situated sufficiently close to each other on a chromosome to be inherited together, i.e. not to be separated by crossing over at meiosis.
Linkage map: A diagramatic representation of the location of genes on the genome, based on the frequency of recombination (and thus on the tightness of linkage).
Linkage disequilibrium: Where a population is not in a state of linkage equilibrium.
Linkage equilibrium: Where, within a population, there is no overall tendency for particular genes to be linked. This state is typical of a large population allowed to mate freely.
Locus: Position at which a gene is located on a chromosome.
LOD: Calculated on the basis of linkage data, a statistically computed estimate of the likelihood of a QTL being present at a particular location on the genome.
Lytic enzyme: An enzyme causing the breakdown of cells or cell components.
Marker: A character or gene which, by virtue of linkage, can be used to indicate the presence of another gene.
Megagametophyte: The female gametophyte.
Meiosis: The special cell division at which the diploid complement of chromosomes is halved, leading to formation of the gametes.
Micropropagation: The vegetative propagation of plants in vitro.
Microsatellite: DNA sequences composed of a tandem repetition of a simple short sequence (frequently a dinucleotide), occurring in the genome of many higher organisms.
Microspore: The cell from which a pollen grain develops.
Mitochondrion: An organelle occurring in the cytoplasm of all eukaryotes, the site of respiration.
Mitosis: The typical cell division, leading to the formation of daughter cells each with the same number of chromosomes as the parent cell.
mRNA: Messenger RNA. Synthesized from a DNA template to which it is complementary.
Mutation: A chemical change in the DNA molecule.
Nucleotide: A compound comprising a nucleoside linked to phosphoric acid. When polymerised give rise to nucleic acids.
Oligonucleotide: A nucleic acid segment comprising a few nucleotides.
Oncogene: A gene causing cancer.
Parthenocarpy: Production of fruit without seeds.
PCR: The polymerase chain reaction. Amplification of DNA through cycles of denaturation (by heating) and synthesis of new strands. Facilitated by the availability of a heat-stable polymerase.
PEG: Polyethylene Glycol.
Ploidy: The number of sets of chromosomes in a cell.
Polymorphism: Where a number of variations occur, e.g. of a particular enzyme, or a number of different alleles at a locus.
Primer: A short oligonucleotide that pairs to a region of single stranded template oligonucleotide.
Probe: A nucleic acid molecule that can be used to detect, by complementary base pairing, another nucleic acid molecule that has a complementary or homologous sequence.
Promoter: A nucleotide sequence that acts as a signal for the binding of RNA polymerase for a particular gene.
Protoplast: A cell without a cell wall.
QTL: Quantitative Trait Locus. A locus contributing to the expression of a polygenic trait.
RAPD: Random Amplified Polymorphic DNA. DNA polymorphisms amplified by arbitrary primers using PCR. Useful as molecular markers.
Recalcitrant seed: Seed which cannot be stored for long periods under the low temperature, dry conditions used for “orthodox” species.
Recognition site: A site, on a nucleic acid molecule, which is recognized by a primer or restriction enzyme.
Recombination: A process leading to the formation of new combinations of genes, e.g. at meiosis.
Restriction endonuclease: An enzyme with the ability to recognize a particular nucleotide sequence and to cleave a DNA molecule at that point.
Restriction fragment: One of the fragments produced by the cleavage of DNA by a restriction enzyme.
Ribozyme: An RNA molecule with the capacity to cleave mRNAs of target genes, thus inhibiting expression of these genes.
RFLP: Restriction Fragment Length Polymorphism. Polymorphisms on the DNA molecule detected by variations in restriction fragments generated by treatment with restriction enzymes.
Segregation: Separation of parental chromosomes at meiosis and of alleles, leading to new gene combinations.
Somaclonal variation: Variation occurring among plants or cells cultured in vitro.
Somatic: The vegetative stages of the cell cycle.
Sporophyte: The diploid spore producing phase in plants.
tDNA: The component of the DNA of Agrobacterium which is integrated into the host genome.
Terpenoid: A class of hydrocarbon occurring in many higher plants.
Transformation: The incorporation of new DNA into a cell's genome.
Transgenic: Referring to the plant or tissue after the incorporation of new DNA.
Translation: The process during which a polypeptide chain is generated from an mRNA template.
Transposible element: A specialised DNA sequence with the capacity to locate at different regions within the genome.