What characterizes genetic imprinting?

• A. It is an epigenetic phenomenon where certain genes are expressed in a parent-of-origin-specific manner due to differential DNA methylation and histone marks.
• B. It is a permanent change in the DNA sequence transmitted to offspring.
• C. It involves RNA editing without affecting DNA.
• D. It occurs only during embryogenesis and not in somatic cells.

Answer: (A)

Genetic imprinting is an epigenetic phenomenon in which certain genes are expressed from only one parental allele, determined by which parent contributed the gene. This parent-of-origin–specific expression is set up by differential DNA methylation and histone modifications at imprinting control regions, which silence one allele while allowing the other to be active. The DNA sequence itself isn’t changed; the imprint is an epigenetic mark that is established during gamete formation and maintained through development, then reset in the germ line for the next generation. This is different from RNA editing, which alters the RNA after transcription, and from a permanent DNA sequence change. While imprinting marks are laid down in gametes, the resulting monoallelic expression can persist in somatic tissues during life, not just in embryogenesis.