<P> The LOD score is calculated as follows: </P> <P> L O D = Z = log 10 ⁡ probability of birth sequence with a given linkage value probability of birth sequence with no linkage = log 10 ⁡ (1 − θ) N R × θ R 0.5 (N R + R) (\ displaystyle (\ begin (aligned) LOD = Z& = \ log _ (10) (\ frac (\ mbox (probability of birth sequence with a given linkage value)) (\ mbox (probability of birth sequence with no linkage))) = \ log _ (10) (\ frac ((1 - \ theta) ^ (NR) \ times \ theta ^ (R)) (0.5 ^ ((NR + R)))) \ end (aligned))) </P> <P> NR denotes the number of non-recombinant offspring, and R denotes the number of recombinant offspring . The reason 0.5 is used in the denominator is that any alleles that are completely unlinked (e.g. alleles on separate chromosomes) have a 50% chance of recombination, due to independent assortment .' θ' is the recombinant fraction, i.e. the fraction of births in which recombination has happened between the studied genetic marker and the putative gene associated with the disease . Thus, it is equal to R / (NR + R) </P> <P> By convention, a LOD score greater than 3.0 is considered evidence for linkage, as it indicates 1000 to 1 odds that the linkage being observed did not occur by chance . On the other hand, a LOD score less than - 2.0 is considered evidence to exclude linkage . Although it is very unlikely that a LOD score of 3 would be obtained from a single pedigree, the mathematical properties of the test allow data from a number of pedigrees to be combined by summing their LOD scores . A LOD score of 3 translates to a p - value of approximately 0.05, and no multiple testing correction (e.g. Bonferroni correction) is required . </P>

What would be the recombination frequency for two genes that are on separate chromosomes