FIGURE 6-34 Linkage-disequilibrium studies of human populations can be used to map genes at high resolution. A new disease mutation arises in the context of an ancestral chromosome among a set of polymorphisms known as the haplotype of that chromosome (indicated by red shading; the blue segments of chromosomes represent general haplotypes derived from the general population and not from the ancestral haplotype in which the mutation originally arose). After many generations, chromosomes that carry the disease mutation will also carry segments of the ancestral haplotype that have not been separated from the disease mutation by recombination. The regions closest to the disease mutation are the most likely to be the ancestral haplotype. This phenomenon is known as linkage disequilibrium. The position of the disease mutation can be located by scanning chromosomes that contain it for highly conserved polymorphisms corresponding to the ancestral haplotype.