Definitions for "Linkage disequilibrium"
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.