Question

'Genetic imprinting', a process of gene silencing, is postulated to be caused by-

• A. Differential rate of replication
• B. Differential states of methylation
• C. Absence of complementary allele
• D. Non-inheritance of the target allele

Hint:

Genomic imprinting is a classic example of epigenetic gene silencing, and its primary molecular signature is differential DNA methylation of alleles depending on their parental origin.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Genomic imprinting is an epigenetic phenomenon in which genes are expressed in a parent-of-origin-specific manner.
It results in the silencing of one of the two inherited parental alleles, leaving only one allele transcriptionally active.

Step 2: Detailed Explanation:
Unlike classical genetic inheritance, genomic imprinting is controlled by epigenetic modifications that alter gene expression without changing the underlying DNA sequence.
The primary molecular mechanism driving genomic imprinting is DNA methylation, which occurs at specific CpG-rich regions called imprinting control regions (ICRs).
During gametogenesis, parent-specific methylation patterns are established on these ICRs.
For an imprinted gene, one parental allele (either maternal or paternal) is heavily methylated, which recruits chromatin-remodeling proteins that condense the local chromatin and silence transcription.
The other parental allele remains unmethylated and transcriptionally active.
Therefore, genomic imprinting is caused by these differential states of DNA methylation between the maternal and paternal alleles.
It does not involve differences in replication rates (A), the absence of a complementary allele (C), or a failure to inherit the gene (D).

Step 3: Final Answer:
The correct option is (B).