direct repeatTwo or more stretches of DNA within a single molecule which have the same nucleotide sequence in the same orientation.
directed amplification of minisatellite DNA(Abbreviation: DAMD). A polymerase chain reaction technique used for obtaining molecular markers in the region of minisatellites .
Directed differentiationManipulating stem cell culture conditions to induce differentiation into a particular cell type.
Directed evolutionA laboratory process used on isolated molecules or microbes to cause mutations and identify subsequent adaptations to novel environments.
Directed mutagenesisThe generation of changes in the nucleotide sequence of a cloned gene by one of several procedures.
Directed sequencingSuccessively sequencing DNA from adjacent stretches of chromosome.
Directional cloningDNA insert and vector molecules are digested with two different restriction enzymes to create noncomplementary sticky ends at either end of each…
disaccharideA dimer consisting of two covalently linked monosaccharides.
disarmThe deletion from a plasmid or virus of genes that are pathogenic.
discontinuous variationVariation where individuals can be classified as belonging to one of a set of discrete, non-overlapping classes.
discordantMembers of a pair showing different, rather than similar, characteristics.
disease resistanceThe genetically determined ability to prevent the reproduction of a pathogen, thereby remaining healthy.
Disease-associated genesAlleles carrying particular DNA sequences associated with the presence of disease.
disease-freeA plant or animal certified through specific tests as being free of specified pathogens .
disease-indexingDisease-indexed organisms have been assayed for the presence of known diseases according to standard testing procedures.
disinfectionAttempted elimination by chemical means of internal micro-organisms (particularly pathogens) from a culture or sample; rarely attained. See: sterilize (1).
disinfestationThe elimination or inhibition of the activity of surface-adhering micro-organisms and removal of insects.
disjunctionSeparation of homologous chromosomes during anaphase I of meiosis, or of sister chromatids during anaphase of mitosis and anaphase II of meiosis.
disomyThe presence of a pair of a specific homologous chromosomes. This is the norm for diploids.
dispenseThe transfer of a measured volume of a solution.
disrupter geneUsed to enforce the sterility of seed saved from a genetically engineered crop. See: genetic use restriction technology.
dissecting microscopeA microscope with a magnifying power of about 50x, used as an aid in the manipulation of small objects, e.g. excision of embryos from young zygotes.
dissectionSeparation of a tissue by cutting into components, for analysis or observation.
distillationThe 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…
disulphide bridgeA chemical bond between pairs of sulphur atoms that stabilizes the three-dimensional structure of proteins, and hence the protein 's normal function.
ditypeIn fungi, a tetrad that contains two kinds of meiotic products (spores), e.g. 2AB and 2ab.
dizygotic twinsTwo-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…
DNAThe molecules inside cells that carry genetic information and pass it from one generation to the next. Also called deoxyribonucleic acid.
DNA (deoxyribonucleic acid)An organic acid and polymer composed of four nitrogenous bases--adenine, thymine, cytosine, and guanine linked via intervening units of phosphate and the…
DNA amplificationMany-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…
DNA amplification fingerprinting(Abbreviation: DAF). A arbitrarily primed polymerase chain reaction technique for obtaining molecular markers using very short (5-8 bp) primers.
DNA bankA service that stores DNA extracted from blood samples or other human tissue.
DNA constructA chimeric DNA molecule, carrying all the genetic information necessary for its transgenic expression in a host cell.
DNA delivery systemA generic term for any procedure that transports DNA into a recipient cell.
DNA diagnosisThe use of DNA polymorphisms to detect the presence of a disease gene.
DNA diagnosticsThe use of DNA polymorphisms to detect the presence of a specific sequence, which could indicate the presence of a contaminant, of a pathogen, or of a…
DNA fingerprintThe unique pattern of DNA fragments identified by Southern hybridization (using a probe that binds to a polymorphic region of DNA) or by polymerase chain…
DNA fingerprintingThe derivation of unique patterns of DNA fragments obtained using a number of marker techniques; historically these were RFLPs, but latterly they are…
DNA helicaseAn enzyme that catalyses the unwinding of the complementary strands of a DNA double helix. Synonym: gyrase.
DNA hybridizationThe annealing of two single-stranded DNA molecules, possibly of different origin, to form a partial or complete double helix.
DNA polymorphismOne of two or more alternate forms (alleles) of a chromosomal locus that differ in nucleotide sequence or have variable numbers of repeated nucleotide…
DNA primaseAn enzyme that catalyses the synthesis of the short strands of RNA that initiate the synthesis of DNA strands.
DNA repairA variety of mechanisms that repair errors (e.g. the incorporation of a non-complementary nucleotide) that occur naturally during DNA replication.
DNA repair genesGenes encoding proteins that correct errors in DNA sequencing.
DNA replication(⦠reh-plih-KAY-shun) The process by which a copy of the DNA in a cell is made before the cell divides.
DNA sequenceThe relative order of base pairs, whether in a DNA fragment, gene, chromosome, or an entire genome. See also: base sequence analysis
DNA sequencingProcedures for determining the nucleotide sequence of a DNA fragment.
DNA topo-isomeraseAn enzyme that catalyses the introduction or removal of supercoils in DNA. Synonym: topo-isomerase.
DollyUnlike the French roulette where the croupier simply points with the stick on the winning number on the table, in the American roulette the croupier uses…
DomainA sub-network of servers and computers within a LAN. Domain information is useful when restoring backup tapes, particularly of email.
DominantAn allele is said to be dominant if it expresses its phenotype even in the presence of a recessive allele. See Allele, Phenotype, Recessive.
Dominant geneA gene whose phenotype is when it is present in a single copy.
dominant marker selectionSelection of cells via a gene encoding a product that enables only the cells that carry the gene to grow under particular conditions.
dominant selectable markerA gene that allows the host cell to survive under conditions where it would otherwise die. Synonym: positive selectable marker.
Dominant(-acting) oncogeneA gene that stimulates cell proliferation and contributes to oncogenesis when present in a single copy. (See Oncogene.)
donor junction siteThe junction between the 5' end of an exon and the 3' end of an intron. See: acceptor junction site.
DormancyA period in which a plant does not grow, awaiting necessary environmental conditions such as temperature, moisture, nutrient availability.
dosage compensationA regulatory mechanism for sex-linked genes, to allow equivalent levels of gene expression from (in mammals) XY or XX genotypes, even though the gene copy…
double crossing-overThe formation of two chiasmata within a chromosome arm, leading to the generation of a double recombinant gamete with respect to genes located within the…
double fertilizationA process, unique to flowering plants, in which two male nuclei, which have travelled down the pollen tube, separately fuse with different female nuclei…
Double helixDescribes the coiling of the antiparallel strands of the DNA molecule, resembling a spiral staircase in which the paired bases form the steps and the…
double recessiveAn organism homozygous for a recessive allele at each of two loci.
double-stranded DNA(Abbreviation: dsDNA ). Two complementary strands of DNA annealed in the form of a double helix. Synonym: duplex DNA.
doubling time(DUH-bling...) In biology, the amount of time it takes for one cell to divide or for a group of cells (such as a tumor) to double in size.
down promoter mutationA mutation that decreases the frequency of initiation of transcription. This leads to a fall in the level of mRNA compared to the wild type state.
down-regulateTo induce genetically a reduction in the level of a gene's expression.
downstreamThe region extending in a 3' direction from a gene.
downstream processingA general term for biotechnological processes which follow the biology, i.e. fermentation of a micro-organism or growth of a plant.
Draft sequenceThe sequence generated by the HGP as of June 2000 that, while incomplete, offers a virtual road map to an estimated 95% of all human genes.
Drosophila melanogasterThe 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…
drugAny substance, other than food, that is used to prevent, diagnose, treat or relieve symptoms of a disease or abnormal condition.
drug deliveryMethod by which a drug is delivered to its site of action. For traditional drugs this is another name for formulation.
dry weightThe weight of tissue obtained following sufficiently prolonged oven-drying at high temperature to remove all water.
dTTPRarely used but strictly correct abbreviation for deoxythymidine 5'-triphosphate. Required for DNA synthesis since it is a direct precursor molecule.
dual cultureA culture made of a plant tissue and one organism (such as a nematode) or an obligate parasite/micro-organism (such as a fungus).