G1 phase

The G₁ phase is a period in the cell cycle during interphase, between mitosis and the S phase. For many cells, this phase is the major period of cell growth during its lifespan. G₁ consists of four subphases:

1. Competence (g1a)
2. Entry (g1a)
3. Progression (g1b)
4. 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 entering the S phase and enter a state of dormancy called the G₀ phase. Most mammallian cells do this.