A 3-month-old male infant presents with severe hypotonia, poor feeding, and failure to thrive. Physical examination reveals small hands and feet, cryptorchidism, and characteristic facial features including almond-shaped eyes and a narrow bifrontal diameter. Genetic testing confirms Prader-Willi syndrome. The underlying mechanism marked as **D** in the pedigree diagram—genomic imprinting disorder—explains why this child's condition results from loss of paternal gene expression in the 15q11-13 region. Which of the following diagnostic approaches is most sensitive for detecting ALL molecular subtypes of this imprinting disorder, including paternal microdeletion, maternal uniparental disomy, and imprinting center defects?