Problem: An infant girl born to a 40-year-old woman is examined by a pediatric resident in the hospital. The pregnancy was uneventful, and there were no complications during the delivery. The physical examination reveals midface hypoplasia with a flat nasal bridge and upslanting palpebral fissures. She has a small mouth and chest auscultation reveals a blowing holosystolic murmur that is best heard along the sternal border. The family history is unremarkable. Karyotype analysis is ordered because the resident suspects a numerical chromosomal disorder, and it shows 3 copies of chromosome 21. Which of the following phenomena is responsible for the infant's condition? Need Assignment Help? Trinucleotide repeat Meiotic non-disjunction Uniparental disomy Genomic imprinting Partial deletion