A 10-month-old female infant presents with seizures that began at 8 months of age, severe developmental delay, and characteristic facial features including a broad beaked nose continuous with a high forehead, widely spaced eyes, and a short philtrum. Karyotype analysis reveals the abnormality marked **A** in the diagram. Which of the following is the MOST appropriate next step in confirming the diagnosis and providing accurate recurrence counseling for the parents?