The tendency for two 'alleles' to be present on the same chromosome (positive LD), or not to segregate together (negative LD). As a result, specific alleles at two different loci are found together more or less than expected by chance. The same situation may exist for more than two alleles. Its magnitude is expressed as the delta (D) value and corresponds to the difference between the expected and the observed haplotype frequency. It can have positive or negative values. LD is decreased by recombination. Thus, it decreases every generation of random mating unless some process opposing the approach to linkage equilibrium. Permanent LD may result from natural selection if some gametic combinations result in higher fitness than other combinations. Link to a lecture on linkage disequilibrium; online linkage disequilibrium analysis.
Describes a condition in which certain alleles at two linked loci are nonrandomly associated with each other. This might be either because of very close physical proximity or because the combination is under some kind of selective pressure.
Where alleles occur together more often than can be accounted for by chance. Indicates that the two alleles are physically close on the DNA strand.
The non-random association between alleles in a population owing to their tendency to be co-inherited.
linkage disequilibrium is often termed "allelic association." When alleles at two distinctive loci occur in gametes more frequently than expected given the known allele frequencies and recombination fraction between the two loci, the alleles are said to be in linkage disequilibrium: evidence for linkage disequilibrium can be helpful in mapping disease genes since it suggests that the two may be very close to one another. [Source: NHBLI/NCBI Glossary
Non-random, non-Mendelian association among polymorphic sites or alleles among loci.
See gametic (phase) disequilibrium.
The condition in which the frequency of a particular haplotype for two loci is significantly greater than that expected from the product of the observed allelic frequencies at each locus.
The occurrence together on the same chromosome of specific alleles at closely linked loci more frequently than would be expected by chance. Because linkage disequilibrium is a function of the distance between loci, it can be used to help infer the order of genes on chromosomes. Using markers on either side of a gene can increase the accuracy of predicting the gene's presence, since two chance crossovers would be very unlikely.
In a population, co-occurrence of a specific DNA marker and a disease at a higher frequency than would be predicted by random chance
Greater co-occurrence of two genetic markers (on the same chromosome, as a haplotype) in a population than would be expected for independent markers. Usually, LD is generated when the markers are located close together on the same chromosome. When variants of two genetic loci are in strong LD, the variant seen at one locus are predictive of the variant found at the other on an individual chromosome.
Where a population is not in a state of linkage equilibrium.
A situation in which some combinations of genetic markers occur more or less frequently in the population than would be expected from their distance apart.
a departure from --Hardy-Weinberg equilibrium due to the fact that sorted alleles are linked, therefore, they don't sort independently.
The tendency of alleles located close to each other on the same chromosome to be inherited together.
the nonrandom association in a pop- ulation of alleles at nearby loci
The frequency, in a population of linked genes, which is governed by factors other than change.
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.
The occurrence, on the same chromosome, of some combinations of alleles of closely linked genes more often than would be predicted by chance.
a measure of linkage between alleles of two different genes.
A condition where two genes are found together in a population at a greater frequency than that predicted simply by the product of their individual gene frequencies.
Linkage disequilibrium is a term used in the study of population genetics for the non-random association of alleles at two or more loci, not necessarily on the same chromosome. It is not the same as linkage, which describes the association of two or more loci on a chromosome with limited recombination between them. Linkage disequilibrium describes a situation in which some combinations of alleles or genetic markers occur more or less frequently in a population than would be expected from a random formation of haplotypes from alleles based on their frequencies.
