What is referred to as differential expression of same gene depending on parent of origin?

Genomic imprinting refers to variation in the expression of a gene or group of genes that depend upon whether those genes came from male or female parent. This term refers to the fact that the process of gametogenesis in one sex apparently marks some genetic material as being different from its counterpa supplied by the opposite sex. Paternal imprinting refers to transcriptional silencing of paternal allele. Example: Prader-Willi syndrome. Maternal imprinting refers to transcriptional silencing of maternal allele. Example: Angelman syndrome. Ref: How the Human Genome Works By Edwin H. McConkey, Page 49; Concepts 0f Genetics (With Cd) By Klug, 7th Edition, Page 127; Harrisson's Principles of Internal Medicine, 18th Edition, Chapter 61