A neonate born at 34 weeks gestation to a 42-year-old mother presents with severe intrauterine growth restriction, multiple congenital anomalies including tetralogy of Fallot, bilateral cleft lip and palate, microcephaly, and horseshoe kidney. Karyotype analysis shows the chromosomal abnormality marked as **B** in the metaphase spread. Which of the following best describes the chromosomal mechanism underlying this condition?