| DNA markers | Segments of chromosomal DNA known to be linked with heritable traits or diseases. Although the markers themselves to not produce the conditions, they exist in concert with the genes responsible and are passed on with them. Certain markers, restriction fragment length polymorphisms, consist of segments of DNA that can be identified on autoradiographs (produced after digestion of the DNA by restriction enzymes and segregation of the resulting fragments through gel electrophoresis). (05 Mar 2000) |
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| DNA-directed DNA polymerase | <enzyme> DNA-dependent DNA polymerases found in bacteria, animal and plant cells. During the replication process, these enzymes catalyze the addition of deoxyribonucleotide residues to the end of a DNA strand in the presence of DNA as template-primer. They also possess exonuclease activity and therefore function in DNA repair. Chemical name: Deoxynucleoside-triphosphate:DNA deoxynucleotidyltransferase (DNA-directed) Registry number: EC 2.7.7.7 (12 Dec 1998) |
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| allotypic marker | Synonym: allotype. (05 Mar 2000) |
| genetic marker | A gene which has an easily identifiable phenotype so that one can tell apart cells or individuals which have the gene and those which do not have it. Such a gene can also be used as a probe to mark cell nuclei or chromosomes so that they can easily be isolated or identified from other nuclei or chromosomes later. (09 Oct 1997) |
| marker | An identifiable physical location on a chromosome (for example, restriction enzyme cuttingsite, gene) whose inheritance can bemonitored. Markers can beexpressed regions of DNA (genes) or some segment of DNA with no knowncoding function but whose pattern of inheritance can be determined. See: restriction fragment length polymorphism. (09 Oct 1997) |
| marker chromosome | An abnormal chromosome that is distinctive in appearance but not fully identified. For example, the fragile x chromosome was once called the marker x. (12 Dec 1998) |
| marker enzyme | <enzyme> An enzyme that is used to identify a specific cell type, cell organelle, or cell component. (05 Mar 2000) |
| marker gene | Gene that confers some readily detectable phenotype on cells carrying the gene, either in culture or in transgenic or chimeric organisms. Gene could be an enzymic reporter gene, a selectable marker conferring antibiotic resistance or a cell membrane protein with a characteristic epitope. (18 Nov 1997) |
| marker locus | A locus on a chromosome or in a stretch of DNA that can be identified (e.g., a restriction fragment length polymorphism) and can serve in linkage analysis and in the isolation of a disease gene. See: linkage marker. (05 Mar 2000) |
| marker, object | <microscopy> A small abrasive stylus, set in a rotating holder mounted on the lower end of the drawtube. The desired part of the specimen is placed in the centre of the field, and the abrasive point is pressed against the slide or cover, and rotated. It describes a tiny circle around the desired object field. (05 Aug 1998) |
| marker trait | A trait that may be of little importance in itself but which by association, linkage, or other means facilitates the detection, anticipation, or understanding of a disease or (for genetic diseases) the localization of the causative gene on the karyotype. (05 Mar 2000) |
| cell marker | <cell biology> Biochemical or genetic characteristics which distinguish and discriminate between different cell types. (26 Mar 1998) |
| cell surface marker | <cell biology> Any molecule characteristic of the plasma membrane of a cell or in some cases of a specific cell type. 5' nucleotidase and Na/K ATPase are often used as plasma membrane markers. (26 Mar 1998) |
| selectable marker | <molecular biology> A gene whose expression allows one to identify cells that have been transforrned or transfected with a vector containing the marker gene. (09 Oct 1997) |
| hypoxanthine-guanine phosphoribosyl tranferase marker | The gene which codes for the enzyme hypoxanthine-guanine phosphoribosyl transferase. It is a selectable marker because cells which have a defective version of this gene are resistant to poisoning by toxic purine derivatives which result from the metabolic pathway that the HGPRT enzyme catalyses. (The purine derivatives are toxic because they incorporate into DNA as a result of the HGPRT enzyme's actions). Because the defective gene cannot produce the enzyme, no toxic purine derivatives are produced, the gene can therefore be selected for. (09 Oct 1997) |
| surrogate marker | <biology> A laboratory measurement of biological activity within the body that indirectly indicates the effect of treatment on disease state. CD4 cell counts and viral load are examples of surrogate markers in HIV infection. (19 Jan 1998) |