If a cell in S phase is fused with a cell in G₁:
1. The G₁ nucleus immediately enters the S phase
2. The S nucleus stops DNA replication
3. The G₁ nucleus directly enters G₂ phase
4. Both nuclei enter the M phase immediately

Cyclins and cyclin-dependent kinases (CDKs) are:
1. Two key classes of regulatory molecules that determine a cell's progress through the cell cycle
2. The products of the proto-oncogenes in a eukaryotic cell
3. Two very important promoters that are involved in oncogenes
4. Mediators of apoptosis

A cell passes the G₁/S transition. This cell will:
1. be allowed to replicate DNA only if there is adequate nutrients and growth signaling.
2. progress through S-phase even if environmental conditions become unfavorable.
3. become quiescent if the environmental conditions become unfavorable.
4. not be subjected to any control check point during the completion of the cycle.

Apart from tissue stem cells, which of the following cells in the human body are good examples of being in reversible G₀ phase?
1. Mature hepatocytes
2. Senescent cells
3. Differentiated muscle
4. Differentiated bone

If an organisms lives in an environment that increases the risk of damage to chromosomes, which of the following would be beneficial?
1. Development of gametes into individuals without fertilization
2. Reproduction by binary fission
3. Syngamy
4. A life cycle excluding meiosis

During which phase of the cell cycle does a mature human RBC replicate its DNA?
1. S phase
2. G₁ phase
3. G₂ phase
4. None