Imprinting can be cell-type specific; for example, this region of chromosome 15 is ONLY imprinted in neurons and a few other specific cell types, but it is not imprinted in most cells in the body, such as bone, liver, and heart cells. Which of the following statements are true about a healthy individual without Prader-Willi or Angelman syndrome? ( Choose two answers)
a. Maternal and paternal copies of SNRPN are expressed at the same level in heart cells.
b. The maternal and paternal copies of UBE3A are differentially expressed in bone cells.
c. The maternal copy of SNRPN has DNA methylation at its promoter in liver cells.
d. Expression of the paternal copy of UBE3A is silenced in neurons.

Genetic imprinting is DNA modifications that result in changing the expression but not the sequence. Factors That affect such changes present both within and outside the cell.

It is a result of the silencing of either maternal or paternal alleles in a pair. This occurs random and leads to phenomenon like X-inactivation. The mechanism involves methylation of the DNA to be silenced. paternal copy of UBE3A is silenced in neurons.