ESTIMATORS FOR PAIRWISE RELATEDNESS AND INDIVIDUAL INBREEDING COEFFICIENTS

Method-of-moments estimators (MMEs) for the two-gene coefficients of r elationship and inbreeding, and for the four-gene Cotterman coefficien ts, are described. These estimators, which use co-dominant genetic mar kers, are most appropriate for estimating pairwise relatedness or indi vidual inbreeding coefficients, as opposed to their mean values in a g roup. This is because, compared to the maximum likelihood estimate (ML E), they show reduced small-sample bias and lack distributional assump tions. The 'efficient' MME is an optimally weighted average of estimat es given by each allele at each locus. Generally, weights must be comp uted numerically, but if true coefficients are assumed zero, simplifie d estimators are obtained whose relative efficiencies are quite high. Population gene frequency is assumed to be assayed in a larger, 'refer ence population' sample, and the biases introduced by small reference samples and/or genetic drift of the reference population are discussed . Individual-level estimates of relatedness or inbreeding, while displ aying high variance, are useful in several applications as a covariate in population studies.