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Epigenetic modifications serve as an extension of the information content by which the underlying genetic code may be interpreted. These modifications mark genomic regions and act as heritable and stable instructions for the specification of chromatin organisation and structure that dictate transcriptional states. In mammals, DNA methylation and the modification of histones account for the major epigenetic alterations. Two cycles of DNA methylation reprogramming have been characterised. During germ cell development, epigenetic reprogramming of DNA methylation resets parent-of-origin based genomic imprints and restores totipotency to gametes. On fertilisation, the second cycle is triggered resulting in an asymmetric difference between parental genomes. Further epigenetic asymmetry is evident in the establishment of the first two lineages at the blastocyst stage. This differentiative event sets the epigenetic …