Dosage compensation in Drosophila melanogaster By what mechanism do male fruit flies balance X-linked gene expression relative to females?
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AHypertranscription (upregulation) of the male X chromosome
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BHypotranscription (downregulation) of both female X chromosomes
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CX-chromosome inactivation in females (Barr body formation)
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DChimerism across somatic tissues
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EGenomic imprinting of X-linked genes only
Answer
Correct Answer: Hypertranscription (upregulation) of the male X chromosome
Explanation
Introduction / Context:Different animals solve X-chromosome dosage problems differently. Mammals inactivate one X in females; Drosophila males upregulate their single X. Identifying species-specific strategies is a fundamental comparative genetics concept.
Given Data / Assumptions:
- Males are XY (one X), females XX (two Xs).
- Dosage compensation equalizes X-linked gene expression between sexes.
- We are focusing on Drosophila, not mammals.
Concept / Approach:In flies, the Male-Specific Lethal (MSL) complex binds the male X chromosome and increases transcription approximately twofold so that male X-linked expression matches that of the two female X chromosomes.
Step-by-Step Solution:
Recognize species: Drosophila uses upregulation, not X-inactivation.Select the option that states hypertranscription of the male X.Exclude mammalian mechanisms (X-inactivation) and unrelated phenomena.Verification / Alternative check:Genomic and chromatin studies show enrichment of MSL complex and histone acetylation (e.g., H4K16ac) on the male X, consistent with elevated transcription.
Why Other Options Are Wrong:
- Hypotranscription of female Xs is not how Drosophila compensates.
- X inactivation is mammalian, not Drosophila.
- Chimerism/imprinting do not explain global dosage compensation in flies.
Common Pitfalls:Overgeneralizing mammalian X-inactivation to all animals.
Final Answer:Hypertranscription (upregulation) of the male X chromosome