Final answer:
Rb and p53 are the two genes that secrete checkpoint proteins in the cell cycle. They play a crucial role in regulating the cell cycle and preventing the division of cells with damaged DNA.
Step-by-step explanation:
The two genes that secrete checkpoint proteins in the cell cycle are Rb and p53. These genes play a crucial role in regulating the cell cycle and preventing the division of cells with damaged DNA. Rb acts at the G₁ checkpoint, while p53 acts when there is damaged DNA in cells undergoing the preparatory processes during G₁. If damaged DNA is detected, p53 halts the cell cycle and can trigger apoptosis if the DNA cannot be repaired. On the other hand, Rb plays a role in regulating the commitment of a cell to division.