Linkage disequilibrium is the condition in which the haplotype frequencies in a population deviate from the values they would have if the genes at each locus were combined at random.
When there is no such deviation, when linkage disequilibrium = 0, then the population is said to be in linkage equilibrium.
The butterfly Papilio memnon (pictured opposite) is an example of high linkage disequilibrium.
How do we calculate linkage disequilibrium?
What causes linkage disequilibrium?