Biology Forums - Study Force

Suppose that a couple has two daughters, Jessica and Robin. Jessica has one normal
Rb gene and one copy that has a nonsense mutation. Robin has two normal copies of
Rb.

(a) What needs to happen in order for Jessica to develop retinoblastoma (a cancer of
the retina)?

(b) What needs to happen in order for Robin to develop retinoblastoma?

Patients with two defective retinoblastoma alleles invariably develop retinoblatomas, leading to its discovery as a tumor suppressor. Rb binds to E2F and represses its activation function. Rb is deactivated upon phosphorylation by mid G1 cyclin-CDKs (and, eventually, late G1 cyclin-CDKs). E2F is a transcriptional activator for a litany of genes required for DNA synthesis. If Rb is mutated, then E2F is not properly inhibited and the genome replication can get out of control. Cancer cells proceed through the cell cycle very rapidly and thus need this sort of high levels of DNA synthesis.


To develop sporadic retinoblastoma, both copies of the Rb gene need to be inactivated through a mutation in each copy of the Rb gene.