Birgid Schlindwein's
Hypermedia Glossary Of Genetic Terms
Search Results
Birgid Schlindwein'sHypermedia Glossary Of Genetic TermsSearch Results |
|
| see Disclaimer |
| 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. |
| Haplotype | A set of closely linked genetic markers present on one chromosome which tend to be inherited together (not easily separable by recombination). Some haplotypes may be in linkage disequilibrium. |
| Population | A group of organisms of the same species relatively isolated from other groups of the same species. See deme. |
| 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. |
| 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. |
| Allele | The term coined by Bateson and Saunders (1902) for characters which are alternative to one another in Mendelian inheritance (Gk. Allelon, one another; morphe, form). Now the term allele is used for two or more alternative forms of a gene resulting in different gene products and thus different phenotypes. In a haploid set of chromosomes there is only one allele at its specific locus. Diploid organisms have 2 alleles at a given locus, i.e. a normal and a mutant allele. A single allele for each gene locus is inherited separately from each parent (e.g., at a locus for eye colour the allele might result in blue or brown eyes). An organism is homozygous for a gene if the alleles are identical, and heterozygous if they are different. |
| Crossing over | The term coined by Morgan and Cattell (1912) for the occurrence of new combinations of linked characters. With the acceptance of the chromosome theory, the term is applied to the breaking during meiosis of one maternal and one paternal chromosome, the exchange of corresponding sections of DNA, and the rejoining of the chromosomes. This process can result in an exchange of alleles between chromosomes and gives rise to new character combinations. Compare recombination. |
| 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. |
| 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. |