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Hypermedia Glossary Of Genetic Terms

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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.
Related Terms:
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.
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.
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.
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.
Locus The position of a gene on a chromosome or other chromosome markers; also, the DNA at that position. The use of the term locus is sometimes restricted to main regions of DNA that are expressed. Plural: loci. See gene expression.
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.
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.

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© Dr. Birgid B. Schlindwein
last update of the database 10/01/2006