Imprinting (parental genomic imprint) involves epigenetic modification of allele of a gene depending on its origin (from the father or the mother), and thus silenced one allele. Differences occur in the parental genomes during gametogenesis as germline-specific DNA methylation patterns in certain sections of the chromosomes. Most imprintowanych gene clusters present in the clear. Each is coded at least one molecule of RNA that is not translated. So far managed to establish two mechanisms of gene silencing in mammals for only three imprintowanych clusters.