What is the key difference between a cis- and trans-epigenetic mechanism that maintains an epigenetic modification? In

Question:

What is the key difference between a cis- and trans-epigenetic mechanism that maintains an epigenetic modification? In Chapter 5, we considered genomic imprinting of the Igf2 gene in which offspring express the copy of the gene they inherit from their father, but not the copy they inherit from their mother. Is this a cis- or trans-epigenetic mechanism?