The expression of a single allele is associated with which of the following?

Question

BlackTom AI · Accepted Answer

Genomic imprinting causes expression of only one parental allele, so it is the correct choice.

1. Relevant knowledge points and concepts
- Alleles: different versions of a gene at the same locus. Normally both parental alleles can be expressed (biallelic expression).
- Monoallelic expression: only one allele is expressed. Two main types: random monoallelic expression (e.g., X‑inactivation, some autosomal genes) and parent‑of‑origin monoallelic expression (genomic imprinting).
- Genomic imprinting: an epigenetic mechanism (DNA methylation, histone modifications at imprinting control regions) established in the germline that silences one parental allele permanently in the offspring, so only the other parental allele is transcribed.
- Examples: Igf2 is expressed only from the paternal allele; H19 only from the maternal allele. Imprinting underlies disorders such as Prader–Willi and Angelman syndromes depending on which parent’s allele is silenced or deleted.

2. Step‑by‑step reasoning
- The question asks which option is associated with expression of a single allele (monoallelic expression).
- X‑inactivation also produces monoallelic expression, but it is random in each cell and serves dosage compensation in females; different cells may express different parental Xs, producing mosaicism.
- Genomic imprinting produces consistent monoallelic expression across cells based specifically on parent of origin (always the maternal or paternal allele is silent for that gene).
- Maternal inheritance and extra‑nuclear inheritance refer to transmission of organelle genomes (mitochondria/chloroplasts), not selective expression of one nuclear allele.

3. Calculations
- No numerical calculations apply.

4. Why the correct answer is correct
- Genomic imprinting directly describes the biological phenomenon where only one allele (either maternal or paternal) is expressed while the other is epigenetically silenced; this matches “expression of a single allele” exactly.

5. Why the other options are incorrect
- X‑inactivation: causes monoallelic expression per cell but is random across cells (not parent‑of‑origin single‑allele expression across the organism).
- Maternal inheritance / Extra‑nuclear inheritance: concern transmission of non‑nuclear genomes (mitochondrial/chloroplast), not selective expression of one nuclear allele.

6. Conclusion
- Therefore, the correct answer is Genomic imprinting, which matches the provided answer.

The expression of a single allele is associated with which of the following?Single choice

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