Leonard Schalkwyk studied allele-specific methylation in humans (Schalkwyk et al. 2010) . He estimated that potentially more than 35,000 sites in the genome exhibit allele-specific modifications, and of these 10% are not in cis, a number that largely exceeds the number of known imprinted loci. These findings suggest that individual genetic heterogeneity may be much larger than estimated thus far and may contribute to individual phenotypic differences. Jiri Forejt used inter-subspecific consomic strains (Gregorova et al. 2008) to investigate male sterility and its consequences for interspecies hybrid sterility (Mihola et al. 2009 ). Furthermore, in the livers of inter-subspecific hybrid strains he discovered new patterns of gene expression that were absent from both parental strains.