The logarithm of the odds of linkage between two loci. Calculated from pedigree data, as the log (to base 10) of the ratio of the probability of the observed pedigree assuming linkage with a specified recombination fraction , to the probability of the observed pedigree assuming no linkage, i.e., recombination fraction = 0.5. A lod score (also called a z value) is thus calculated as z = log₁₀ (Prob(data