genetic linkage

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link·age

(lingk'ăj),
1. A chemical covalent bond.
2. The relationship between syntenic loci sufficiently close that the respective alleles are not inherited independently by the offspring; a characteristic of loci, not genes.
Genetic linkageclick for a larger image
Fig. 170 Genetic linkage . The phenotypes produced by a testcross.

genetic linkage

the association between genes located (linked) on the same chromosome, thus producing proportions of gametes that are not those expected by INDEPENDENT ASSORTMENT although, unless there is very close linkage, the same TYPES of gamete will be produced. Instead, there tends to be association of particular alleles together in the gametes (the ‘parental’ types, in the same combination as the parent), with other combinations being less frequent (see RECOMBINATION and CROSSING OVER). By convention the amount of recombination between linked genes is a direct measure of their distance apart along the chromosome, 1% recombination being equivalent to the MAP UNIT. The amount of recombination occuring is best measured in a TESTCROSS calculated from the total number of recombinant types in the testcross progeny as a proportion of the total progeny. For example, a testcross with genes in COUPLING produced the PHENOTYPES in Fig. 170 where the amount of recombination would be:

and the genes A and B could be represented on a GENETIC MAP as:

Had the two genes been independently assorting (i.e., on different chromosomes) roughly equal numbers of each phenotype would have been expected in the progeny (about 70). Similarly, since the maximum expected amount of recombination between two genes is 50%, if two genes are located more than 50 map units apart on the same chromosome they will appear to be independent of each other.

References in periodicals archive ?
AFLP markers of the three types were used to construct the genetic linkage map for Phalaenopsis, and types 1, 3 for Phalaenopsis '462', types 2 and 3 for Phalaenopsis '20', following the methods of Grattapaglia and Sederoff (1994).
ABSTRACT A genetic linkage map of the blood clam (Tegillarca granosa) was constructed based on simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers.
This genetic linkage map showed similar genetic distances and same genetic marker orders compared with the chicken consensus linkage map (Groenen et al.
Tenders are invited for Purchase Of Genetic Linkage Map And Mapping Quantitative Trait Loci (Qtls) Software
Jawali (2010) Construction of genetic linkage map of bread wheat (Triticum aestivum L.
Washington, July 29 (ANI): A team of scientists has constructed a first-generation genetic linkage map for the saltwater crocodile Crocodylus porosus.
The number of available markers remains small and inadequate for genomic-wide mapping analysis, and no genetic linkage map has been published for any species.
AUSTRALIAN scientists are working with colleagues in Thailand, Hong Kong, France and the United States to construct a genetic linkage map of the tiger prawn genome.
A genetic linkage map consisting of 343 RFLP, STS, and RAPD markers was constructed based on a subset (90) of the [F.