A 5-month-old girl has bilateral retinoblastoma. Neither parent has a history of having had retinoblastoma. Chromosomal analysis of the patient’s stimulated peripheral blood lymphocytes is done; the photograph is of a representative karyotype. Which of the following critical events has most likely resulted from an aberration involving chromosome 13?
A. Proto-oncogene activation
B. Proto-oncogene amplification
C. Proto-oncogene loss
D. Tumor-suppressor gene activation
E. Tumor-suppressor gene loss