Dosage compensation in Drosophila melanogaster By what mechanism do male fruit flies balance X-linked gene expression relative to females?

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:

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