Question 1
What aberrant change causes the abnormal growth in retinoblastoma?
◦ Proto-oncogenes are changed to oncogenes.
◦ The tumor-suppressor gene is turned off.
◦ Genetic amplification causes the growth.
◦ Chromosomes 9 and 21 are fused.
Question 2
Why are two “hits” required to inactivate tumor-suppressor genes?
◦ Each allele must be altered, and each person has two copies, or alleles, of each gene, one from each parent.
◦ The first hit stops tissue growth, and the second hit is needed to cause abnormal tissue growth.
◦ Tumor-suppressor genes are larger than proto-oncogenes, requiring two hits to affect carcinogenesis.
◦ The first hit is insufficient to cause enough damage to cause a mutation.