We define ‘genetic individuality’ as intraspecies variation that has substantial heritability and involves traits that are sufficiently common that they can be observed in any modest–sized sampling of individuals. We propose that genetic individuality is largely shaped by the combinatory shuffling of a modest number of genes, each of which exists as a family of functionally and structurally diverged alleles. Unequivocal examples of such allele families are found at the O–antigen–biosynthetic locus inPseudomonas aeruginosaand the human leucocyte antigen locus in humans. We examine characteristic features of these allele families and explore the possibility that genetic loci with similar characteristics can be recognized in a whole–genome scan of human genetic variation.