are nearby are often correlated. To the degree that two variants are correlated, knowing one's genotype at one location also tells you something, albeit probabilistic, about what their genotype will be at the other location. This is because any time a mutation (a new variant in the human genome) occurs, it occurs on a specific chromosome background. Thus, at the time it occurs the new variant is perfectly correlated with all the other variants that exist on that chromosome. As the chromosome containing the mutation is transmitted to offspring across several generations, recombination will cause alleles at marker loci that are further from the mutation to be interchanged. This is because genetic variants that are further apart are more likely to be broken up due to recombination events. Genetic variants that are closer together are far less likely to have a recombination occur between them, leading to a higher correlation between the alleles at those nearby marker locations. Accordingly, the associated genetic background surrounding the mutation will become progressively smaller (Figure 2). In general, the closer the marker is to the novel variant, the stronger the LD will be (Jorde, 1995), although there is not a perfect correspondence between distance
