A clinical geneticist observes a patient with short stature, webbed neck, and primary amenorrhea. Karyotype analysis reveals 45 chromosomes with a single X chromosome. Which of the following molecular mechanisms best explains why this individual exhibits clinical symptoms despite females normally having one inactivated X chromosome (Barr body)?

Options:

• A: Complete inactivation of both X chromosomes in normal females.
• B: Pseudoautosomal regions on the inactive X chromosome escape inactivation and are required in double dosage for normal development.
• C: The single X chromosome undergoes complete genomic imprinting and is silenced.
• D: Non-disjunction of autosomes masks the expression of genes on the single X chromosome.

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