dGTPAbbreviation for deoxyguanosine 5'-triphosphate. dGTP is required for DNA synthesis since it is a direct precursor molecule. See: guanosine, guanylic acid.
di-deoxynucleotide(Abbreviations: ddNTP,didN). A synthetic deoxynucleotide that lacks a 3'-hydroxyl group, and is thus unable to form the 3'?
DiabetesAny of several diseases in which the kidneys make a large amount of urine. Diabetes usually refers to diabetes mellitus in which there is also a high…
diakinesisA stage of meiosis at the end of prophase I, in which the contraction of the chromosomes is almost at a maximum, pairing configurations are well defined…
dialysis(dye-AL-ih-sis) The process of filtering the blood when the kidneys are not able to cleanse it.
diazotrophAn organism that can fix atmospheric nitrogen.
dichogamyThe condition in which the male and the female reproductive organs of a flower (or certain hermaphroditic animals) mature at different times, thereby…
dicotyledon(Abbreviation: dicot). A plant with two cotyledons . One of the two major classes of flowering plants (along with the monocotyledons ).
Dideoxynucleotide (didN)A deoxynucleotide that lacks a 3' hydroxyl group, and is thus unable to form a 3'-5' phosphodiester bond necessary for chain elongation.
differential centrifugationA method for separating sub-cellular particles according to their sedimentation coefficients, which are roughly proportional to their size.
differential displayA method to identify mRNAs which are present at different levels in different tissues, or in response to specific treatments.
differentially permeableReferring to a membrane, through which different substances diffuse at different rates.
DifferentiationIn cancer, refers to how mature (developed) the cancer cells are in a tumor. Differentiated tumor cells resemble normal cells and tend to grow and spread…
diffusionThe spontaneous movement of molecules from a region of higher concentration to a region of lower concentration.
digestTo cut DNA molecules with one or more restriction endonucleases.
dihaploidAn individual which arises from a doubled haploid.
dihybridAn individual that is heterozygous for two pairs of alleles; the progeny of a cross between homozygous parents differing at two loci.
dimer1. A molecule formed by the covalent combination of two monomers, generally accompanied by elimination of water. 2.
dimethyl sulphoxide(Abbreviation: DMSO). A highly hygroscopic liquid and powerful solvent with little odour, colour or toxicity when pure.
dimorphismThe existence of two distinctly different types of individuals within a species. An obvious example is sexual dimorphism in mammals.
DiploidThe status of having two complete sets of chromosome s, most commonly one set of paternal origin and the other of maternal origin.
Diploid cellA cell which contains two copies of each chromosome. See Haploid cell.
diplonemaStage in prophase I of meiosis following the pachytene stage, but preceding diakinesis, in which one pair of sister chromatids begin to separate from the…
direct embryogenesisThe formation in culture, on the surface of zygotic or somatic embryos or on explant tissues (leaf section, root tip, etc.
direct organogenesisFormation of organs directly on the surface of cultured intact explants . The process does not involve callus formation. Opposite: indirect organogenesis.
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 mutagenesisThe generation of changes in the nucleotide sequence of a cloned gene by one of several procedures.
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-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 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 replication(⦠reh-plih-KAY-shun) The process by which a copy of the DNA in a cell is made before the cell divides.
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.)