genetic linkage


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Related to genetic linkage: genetic map, Complete linkage

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 ?
The genetic linkage map of Phalaenopsis '462' consisted of 122 markers (104 for the male parent, 18 for co-parents) in 15 linkage groups, and had a total genetic distance of 820.
Order correlations among genetic rates obtained from data in the original scale and with scale transformation for data structures without and with heterogeneity among the cattle herds with and without genetic linkage were very similar in all animal categories.
To extend the family studies of these disorders and systematically identify genetic regions that contribute to alcohol dependence, habitual smoking, or both, COGA researchers used a method known as genetic linkage analysis.
Genetic linkage of attention-deficit/hyperactivity disorder on chromosome 16p13, in a region implicated in autism.
The development of genetic linkage maps is particularly useful for the mapping of quantitative trait loci (QTLs) and for markerassisted selection (MAS) (Lander and Botstein, 1989; Cho er al.
A fascinating account of research on mitochondrial DNA, the source of matriarchal genetic linkage from generation to generation.
Illumina will collaborate with Oxagen to map SNP dusters in genetic linkage regions .
Dr Mac Armstrong said: "We want to get research diverted into other causes of autism - there is plenty of fertile ground, not least the genetic linkage.
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.
Genetic linkage maps provide an organizational framework for genes and phenotypes in the genome (9).