Figure 1.

Positive LD exists on a spectrum influenced by several factors potentially affecting recombination rate (r) among loci. D’ is a normalized metric of LD. For positive LD it is represented by the function D’ = (x_aa − p_a × q_a)/min(x_ab, x_ba), whereby x is haplotype frequency and p and q are allele frequencies for two polymorphic loci with 2 alleles (a, b) each. Rather than a mechanistically accurate diagram, consider this figure as a roughly organized corkboard onto which the various factors and conditions have been pinned.