The G1 phase is the primary growth phase for a eukaryotic cell. For many cells, this phase is the major period of cell growth during it's lifespan. Consists of four subphases:
  • Competance (G1a)
  • Entry (G1b)
  • Progression (G1c)
  • Assembly (G1d)

These subphases may be affected by limiting growth factors, nutrient supply, and additional inhibiting factors. A cell may pause in the G1 phase before endering the S phase and enter a state of dormancy called the G0 phase.

It is part of the cell cycle, and followed by the S phase