Genetic links among individuals are widely used to characterize the diversity of domesticated and natural populations and they also provide complementary information for statistical population summaries. We first discuss the measures used by geneticists based on genealogy and DNA data. The choice of metrics of genetic links should be coherent with the objectives: biodiversity or genotype-phenotype relationships. For the last objective, we evaluate by simulation the interest of genetic distances when the objective is the prediction of individual genetic values and phenotypes using kernel regression. A pseudo-distance based on correlations between marker genotypes of pairs of individual yields better predictions than other classical definition of distances.