Birgid Schlindwein's
Hypermedia Glossary Of Genetic Terms
Search Results
Birgid Schlindwein'sHypermedia Glossary Of Genetic TermsSearch Results |
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| Linkage | An association in inheritance between characters such that the parental character combinations appear among the progeny more often than the non-parental. The proximity of two or more markers (e.g. genes, RFLP markers) on a chromosome; the closer together the markers are, the lower the probability that they will be separated during DNA repair or replication processes (binary fission in prokaryotes, mitosis or meiosis in eukaryotes), and hence the greater the probability that they will be inherited together. Cf. recombination, complete linkage, partial linkage, non-linkage, linkage equilibrium, linkage disequilibrium. |
| Inheritance | Trait which is derived by an heir from an ancestor; transmission and reception by animal or plant generation. Trait acquired via biological heredity that passes from parent to offspring. | |||||||||||||||||||||
| Trait | An attribute or character of an individual within a species for which heritable differences can be defined. | |||||||||||||||||||||
| Marker | An identifiable physical location on a chromosome (e.g., restriction enzyme cutting site, gene, minisatellite, microsatellite) whose inheritance can be monitored. Markers can be expressed regions of DNA (genes) or some segment of DNA with no known coding function but whose pattern of inheritance can be determined. See RFLP, restriction fragment length polymorphism. | |||||||||||||||||||||
| Gene | The term coined by Johannsen (1909) for the fundamental physical and functional unit of heredity. The word gene was derived from De Vries' term pangen, itself a derivative of the word pangenesis which Darwin (1868) had coined. A gene is an ordered sequence of nucleotides located in a particular position (locus) on a particular chromosome that encodes a specific functional product (the gene product, i.e. a protein or RNA molecule). It includes regions involved in regulation of expression and regions that code for a specific functional product. See gene expression, allele. | |||||||||||||||||||||
| Restriction fragment length polymorphism (RFLP) | Genetic variation between individuals in DNA fragment sizes resulting from a difference in DNA sequence that affects the recognition sequence for restriction enzymes when cut by specific restriction enzymes. When DNA is digested by a particular enzyme the fragment sizes will differ depending on the presence or absence of the proper recognition sequence for the enzyme. Polymorphic sequences that result in RFLPs are used as markers on both physical maps and genetic linkage maps. RFLPs are usually caused by mutation at a cutting site. | |||||||||||||||||||||
| Chromosome | The term was proposed by Waldeyer (1888) for the individual threads within a cell nucleus (gk. chroma, colour; soma, body). The self-replicating genetic structures of cells containing the cellular DNA that bears in its nucleotide sequence the linear array of genes. In prokaryotes, chromosomal DNA is circular, and the entire genome is carried on one chromosome. Eukaryotic genomes consist of a number of chromosomes whose DNA is associated with different kinds of proteins. | |||||||||||||||||||||
| Probability | The expectation of the occurrence of a particular event. Likelihood of the occurrence of any event in the doctrine of chances, or the ratio of the number of favorable chances to the whole number of chances, favorable and unfavorable. | |||||||||||||||||||||
| Prokaryote | Cell or organism lacking a membrane-bound, structurally discrete nucleus and other subcellular compartments. Bacteria are prokaryotes. Compare eukaryote. See chromosomes. | |||||||||||||||||||||
| Mitosis | The most frequent process of nuclear division (karyokinesis) in cells that produces daughter cells that are genetically identical to each other and to the parent cell. The mitosis is divided into four (or five) phases: prophase, prometaphase, metaphase, anaphase, telophase. Mitosis and interphase make the cell cylcle. | |||||||||||||||||||||
| Meiosis | The term coined by Farmer and Moore (1905) for the process of two consecutive cell divisions in the diploid progenitors of sex cells. Meiosis results in four rather than two daughter cells (gametes), each with a haploid set of each chromosome pair. In meiosis I the prophase is more complex than that of mitosis. Five different stages can be differentiated: leptotene, zygotene, pachytene, diplotene and diakinesis. Prophase is followed by metaphase I, anaphase I, telophase I and interkinesis. Meiosis II could be described as a haploid mitosis resulting in four haploid gametes.
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| Eukaryote | Cell or organism with membrane-bound, structurally discrete nucleus and other well-developed subcellular compartments. Eukaryotes include all organisms except viruses, bacteria, and blue-green algae. Compare prokaryote. See chromosomes. | |||||||||||||||||||||
| Recombination | The process by which progeny derive a combination of linked genes different from that of either parent. In higher organisms, this can occur by crossing over between their loci during meiosis. Recombination may come about through random orientation of non-homologous chromosome pairs on the meiotic spindles, from crossing-over between homologous chromosomes, from gene conversion, or by other means. See homologous recombination. | |||||||||||||||||||||
| Complete linkage | Complete linkage describes the inheritance patterns for two genes on the same chromosome when the observed frequency for crossing over between the loci is zero. See linkage, non-linkage, partial linkage. | |||||||||||||||||||||
| Partial linkage | Partial linkage describes one of the inheritance patterns for two genes on the same chromosome, when the expected frequency for crossing over between the loci is greater than zero but less than one. From partial linkage analysis the order and spacing of genes on the same chromosome can be concluded. See linkage, complete linkage, non-linkage. | |||||||||||||||||||||
| Non-linkage | Non-linkage describes the inheritance patterns for two genes on the same chromosome, when the expected frequency for crossing over between the loci is at least one. The observed inheritance pattern for non-linked genes on the same chromosome is the same as for two genes on different chromosomes. See linkage, complete linkage, partial linkage. | |||||||||||||||||||||
| Linkage equilibrium | When the observed frequencies of haplotypes in a population agrees with haplotype frequencies predicted by multiplying the frequencies of individual genetic markers in each haplotype. Cf. linkage disequilibrium. | |||||||||||||||||||||
| Linkage disequilibrium | When the observed frequencies of haplotypes in a population does not agree with haplotype frequencies predicted by multiplying together the frequency of individual genetic markers in each haplotype. This results from a more or less recent mutation in one of two linked alleles. So some allele combinations occure more frequnetly than others. The disequilibrium decreases from generation to generation by crossing over and recombination. Cf. linkage equilibrium. |
