Figure 2.

How LD works. Part 1: the marker locus with multiple alleles is “next to” a coding locus with only one allele (the pentagon). Part 2: a mutation in a single person occurs at what is now becomes the disease locus. The “oval” allele happens to be the marker allele on the DNA strand with the now mutated allele at the disease locus. Part 3: after generations, if there is no recombination between the marker and disease loci, the mutation remains on the same DNA strand with the “oval” allele. The two alleles are “associated.” The alternative is that there is recombination between the loci, and the “oval” allele is no longer the exclusive neighbor of the disease allele, and there is no association. Part 4: other mutations occur at the disease locus. These occur independently of what the allele at the marker locus happens to be, thus degrading any association between that “oval” allele and the disease. Part 5: whether due to recombination or to multiple disease mutations, there is then no association between marker and disease.